--- a/spec/latest/index.html Fri Oct 14 17:34:09 2011 -0400
+++ /dev/null Thu Jan 01 00:00:00 1970 +0000
@@ -1,4334 +0,0 @@
-<!DOCTYPE html>
-<html>
-<head>
-<title>JSON-LD 1.0</title>
-<meta http-equiv="content-type" content="text/html; charset=UTF-8">
-<!--
- === NOTA BENE ===
- For the three scripts below, if your spec resides on dev.w3 you can check them
- out in the same tree and use relative links so that they'll work offline,
- -->
-<script type="text/javascript"
- src="http://dev.w3.org/2009/dap/ReSpec.js/js/respec.js" class="remove">
- </script>
-<script type="text/javascript" class="remove">
-
- var preProc = {
- apply: function(c) {
- // extend the bibliography entries
- berjon.biblio["MICRODATA"] = "Ian Hickson; et al. <a href=\"http://www.w3.org/TR/microdata/\"><cite>Microdata</cite></a> 04 March 2010. W3C Working Draft. URL: <a href=\"http://www.w3.org/TR/microdata/\">http://www.w3.org/TR/microdata/</a> ";
- berjon.biblio["HTML-RDFA"] = "Manu Sporny; et al. <a href=\"http://www.w3.org/TR/rdfa-in-html/\"><cite>HTML+RDFa</cite></a> 04 March 2010. W3C Working Draft. URL: <a href=\"http://www.w3.org/TR/rdfa-in-html/\">http://www.w3.org/TR/rdfa-in-html/</a> ";
- berjon.biblio["BCP47"] = "A. Phillips, M. Davis. <a href=\"http://tools.ietf.org/rfc/bcp/bcp47.txt\"><cite>Tags for Identifying Languages</cite></a> September 2009. IETF Best Current Practice. URL: <a href=\"http://tools.ietf.org/rfc/bcp/bcp47.txt\">http://tools.ietf.org/rfc/bcp/bcp47.txt</a>";
- berjon.biblio["RDF-API"] = "Manu Sporny, Benjamin Adrian, Nathan Rixham; et al. <a href=\"http://www.w3.org/2010/02/rdfa/sources/rdf-api/\"><cite>RDF API</cite></a> Latest. W3C Editor's Draft. URL: <a href=\"http://www.w3.org/2010/02/rdfa/sources/rdf-api/\">http://www.w3.org/2010/02/rdfa/sources/rdf-api/</a>";
- berjon.biblio["RDF-INTERFACES"] = "Nathan Rixham, Manu Sporny, Benjamin Adrian; et al. <a href=\"http://www.w3.org/2010/02/rdfa/sources/rdf-interfaces/\"><cite>RDF Interfaces</cite></a> Latest. W3C Editor's Draft. URL: <a href=\"http://www.w3.org/2010/02/rdfa/sources/rdf-interfaces/\">http://www.w3.org/2010/02/rdfa/sources/rdf-interfaces/</a>";
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- sp.innerHTML = con ;
- p.replaceChild(sp, item) ;
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- // external datatype references
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- p.replaceChild(sp, item) ;
- }
- // now do terms
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- for (var i = 0; i < refs.length; i++) {
- var item = refs[i];
- if (!item) continue ;
- var p = item.parentNode ;
- var con = item.innerHTML ;
- var ref = item.getAttribute('title') ;
- if (!ref) {
- ref = item.textContent ;
- }
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- ref = ref.replace(/\n/g, '_') ;
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- }
- var sp = document.createElement( 'dfn' ) ;
- sp.title = ref ;
- sp.innerHTML = con ;
- p.replaceChild(sp, item) ;
- }
- // now term references
- refs = document.querySelectorAll('tref') ;
- for (var i = 0; i < refs.length; i++) {
- var item = refs[i];
- if (!item) continue ;
- var p = item.parentNode ;
- var con = item.innerHTML ;
- var ref = item.getAttribute('title') ;
- if (!ref) {
- ref = item.textContent ;
- }
- if (ref) {
- ref = ref.replace(/\n/g, '_') ;
- ref = ref.replace(/\s+/g, '_') ;
- }
-
- var sp = document.createElement( 'a' ) ;
- var id = item.textContent ;
- sp.className = 'tref' ;
- sp.title = ref ;
- sp.innerHTML = con ;
- p.replaceChild(sp, item) ;
- }
- }
- } ;
-
-
- var respecConfig = {
- // specification status (e.g. WD, LCWD, NOTE, etc.). If in doubt use ED.
- specStatus: "unofficial",
- //publishDate: "2010-04-29",
- copyrightStart: "2010",
-
- // the specification's short name, as in http://www.w3.org/TR/short-name/
- shortName: "json-ld",
- subtitle: "A Context-based JSON Serialization for Linking Data",
- // if you wish the publication date to be other than today, set this
- // publishDate: "2009-08-06",
-
- // if there is a previously published draft, uncomment this and set its YYYY-MM-DD date
- // and its maturity status
- previousPublishDate: "2011-08-17",
- previousMaturity: "ED",
- previousDiffURI: "http://json-ld.org/spec/ED/20110817/index.html",
- diffTool: "http://www.aptest.com/standards/htmldiff/htmldiff.pl",
-
- // if there a publicly available Editor's Draft, this is the link
- edDraftURI: "http://json-ld.org/spec/latest/",
-
- // if this is a LCWD, uncomment and set the end of its review period
- // lcEnd: "2009-08-05",
-
- // if you want to have extra CSS, append them to this list
- // it is recommended that the respec.css stylesheet be kept
- extraCSS: [
- "http://dev.w3.org/2009/dap/ReSpec.js/css/respec.css",
- "spec.css"
- ],
-
- // editors, add as many as you like
- // only "name" is required
- editors: [
- { name: "Manu Sporny", url: "http://manu.sporny.org/",
- company: "Digital Bazaar", companyURL: "http://digitalbazaar.com/" },
- { name: "Gregg Kellogg", url: "http://greggkellogg.net/",
- company: "Kellogg Associates" },
- { name: "Dave Longley", url: "http://digitalbazaar.com/",
- company: "Digital Bazaar", companyURL: "http://digitalbazaar.com/"}
- ],
-
- // authors, add as many as you like.
- // This is optional, uncomment if you have authors as well as editors.
- // only "name" is required. Same format as editors.
-
- authors: [
- { name: "Manu Sporny", url: "http://digitalbazaar.com/",
- company: "Digital Bazaar", companyURL: "http://digitalbazaar.com/" },
- { name: "Gregg Kellogg", url: "http://greggkellogg.net/",
- company: "Kellogg Associates" },
- { name: "Dave Longley", url: "http://digitalbazaar.com/",
- company: "Digital Bazaar", companyURL: "http://digitalbazaar.com/"},
- { name: "Mark Birbeck", url: "http://webbackplane.com/",
- company: "Backplane Ltd.", companyURL: "http://webbackplane.com/" },
- ],
-
- // name of the WG
- wg: "Linking Data in JSON Community Group",
-
- // URI of the public WG page
- wgURI: "http://json-ld.org/",
-
- // name (with the @w3c.org) of the public mailing to which comments are due
- wgPublicList: "public-linked-json@w3c.org",
-
- // URI of the patent status for this WG, for Rec-track documents
- // !!!! IMPORTANT !!!!
- // This is important for Rec-track documents, do not copy a patent URI from a random
- // document unless you know what you're doing. If in doubt ask your friendly neighbourhood
- // Team Contact.
- wgPatentURI: "",
- maxTocLevel: 4,
- preProcess: [ preProc ],
- alternateFormats: [ {uri: "diff-20110817.html", label: "diff to previous version"} ],
- };
-
- function updateExample(doc, content) {
- // perform transformations to make it render and prettier
- content = content.replace(/<!--/, '');
- content = content.replace(/-->/, '');
- content = doc._esc(content);
- content = content.replace(/\*\*\*\*([^*]*)\*\*\*\*/g, '<span class="diff">$1</span>') ;
- return content ;
- }
-
- function updateDTD(doc, content) {
- // perform transformations to
- // make it render and prettier
- content = '<pre class="dtd">' + doc._esc(content) + '</pre>';
- content = content.replace(/!ENTITY % ([^ \t\r\n]*)/g, '!ENTITY <span class="entity">% $1</span>');
- content = content.replace(/!ELEMENT ([^ \t$]*)/mg, '!ELEMENT <span class="element">$1</span>');
- return content;
- }
-
- function updateSchema(doc, content) {
- // perform transformations to
- // make it render and prettier
- content = '<pre class="dtd">' + doc._esc(content) + '</pre>';
- content = content.replace(/<xs:element\s+name="([^&]*)"/g, '<xs:element name="<span class="element" id="schema_element_$1">$1</span>"') ;
- return content;
- }
-
- function updateTTL(doc, content) {
- // perform transformations to
- // make it render and prettier
- content = '<pre class="sh_sourceCode">' + doc._esc(content) + '</pre>';
- content = content.replace(/@prefix/g, '<span class="sh_keyword">@prefix</span>');
- return content;
- }
- </script>
-<style>
-.diff { font-weight:bold; color:#0a3; }
-ol.algorithm.update { margin-left: 2em; }
-ol.algorithm.update>li { list-style-type: none; }
-ol.algorithm.update>li>span.list-number {
- display:block;
- float: left;
- margin-left: -3.5em;
-}
-</style>
-</head>
-
-<body>
-<section id="abstract">
-<p>
-JSON [[!RFC4627]] has proven to be a highly useful object serialization and
-messaging format. In an attempt to harmonize the representation of Linked Data
-in JSON, this specification outlines a common JSON representation format for
-expressing directed graphs; mixing both Linked Data and non-Linked Data in
-a single document.
-</p>
-</section>
-
-<section id='sotd'>
-<p>This document is an experimental work in progress.</p>
-<!-- <p>
-This document has been reviewed by W3C Members, by software
-developers, and by other W3C groups and interested parties, and is
-endorsed by the Director as a W3C Recommendation. It is a stable
-document and may be used as reference material or cited from another
-document. W3C's role in making the Recommendation is to draw attention
-to the specification and to promote its widespread deployment. This
-enhances the functionality and interoperability of the Web.
-</p> -->
-</section>
-
-<section>
-<h1>Introduction</h1>
-
-<p>
-JSON, as specified in [[!RFC4627]], is a simple language for representing
-data on the Web. Linked Data is a technique for creating a graph of interlinked data across
-different
-documents or Web sites. Data entities are described using <tref>IRI</tref>s,
-which are typically dereferencable and thus may be used to find more
-information about an entity, creating a "Web of Knowledge". JSON-LD is intended to be a simple
-publishing method for expressing not only Linked Data in JSON, but also for adding
-semantics to existing JSON.
-</p>
-
-<p>
-JSON-LD is designed as a light-weight syntax that can be used to express
-Linked Data. It is primarily intended to be a way to use Linked Data
-in Javascript and other Web-based programming environments. It is also
-useful when building interoperable Web services and when storing Linked
-Data in JSON-based document storage engines. It is practical and designed
-to be as simple as possible, utilizing the large number of JSON parsers
-and libraries available today. It is designed to be able to
-express key-value pairs, RDF data, RDFa [[RDFA-CORE]] data, Microformats
-[[MICROFORMATS]] data, and Microdata [[MICRODATA]]. That is, it supports
-every major Web-based structured data model in use today.
-</p>
-
-<p>
-The syntax does not necessarily require applications to change their JSON, but
-allows to easily add meaning by adding context in a way that is either in-band or
-out-of-band. The syntax is designed to not disturb already deployed systems
-running on JSON, but provide a smooth upgrade path from JSON to JSON with
-added semantics. Finally, the format is intended to be easy to parse, efficient to
-generate, convertible to RDF in one pass, and require a very small memory footprint
-in order to operate.
-</p>
-
-<section>
-<h2>How to Read this Document</h2>
-
-<p>
-This document is a detailed specification for a serialization of Linked
-Data in JSON. The document is primarily intended for the following audiences:
-</p>
-
-<ul>
- <li>Web developers that want to understand the design decisions and
- language syntax for JSON-LD.</li>
- <li>Software developers that want to encode Microformats, RDFa, or Microdata
- in a way that is cross-language compatible via JSON.</li>
- <li>Software developers that want to implement processors and APIs for
- JSON-LD.</li>
-</ul>
-
-<p>
-To understand the basics in this specification you must first be familiar with
-JSON, which is detailed in [[!RFC4627]]. To understand the API and how it is
-intended to operate in a programming environment, it is useful to have working
-knowledge of the JavaScript programming language [[ECMA-262]] and
-WebIDL [[!WEBIDL]]. To understand how JSON-LD maps to RDF, it is helpful to be
-familiar with the basic RDF concepts [[!RDF-CONCEPTS]].</p>
-
-<p>
- Examples may contain references to existing vocabularies and use <tref>prefix</tref>es to refer to Web Vocabularies. The following is a list of all vocabularies and their <tref>prefix</tref> abbreviations, as used in this document:
-</p>
-<ul>
- <li>The <a href="http://purl.org/dc/terms/">Dublin Core</a>
- vocabulary (abbreviation: <code>dc</code>, e.g., <code>dc:title</code>)</li>
- <li>The <a href="http://xmlns.com/foaf/0.1/">Friend of a Friend</a>
- vocabulary (abbreviation: <code>foaf</code>, e.g., <code>foaf:knows</code>)</li>
- <li>The <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#">RDF</a>
- vocabulary (abbreviation: <code>rdf</code>, e.g., <code>rdf:type</code>)</li>
- <li>The <a href="http://www.w3.org/2001/XMLSchema#">XSD</a>
- vocabulary (abbreviation: <code>xsd</code>, e.g., <code>xsd:integer</code>)</li>
-</ul>
-
-<p>
- JSON [[RFC4627]] defines several terms which are used throughout this document:
- <dl>
- <dt><tdef>JSON Object</tdef></dt><dd>
- An object structure is represented as a pair of curly brackets surrounding zero or
- more name/value pairs (or members). A name is a <tref>string</tref>. A single colon comes after
- each name, separating the name from the value. A single comma separates a value
- from a following name. The names within an object SHOULD be unique.
- </dd>
- <dt><tdef>array</tdef></dt>
- <dd>
- An array is an ordered collection of values. An array structure is represented as square brackets surrounding zero or more values (or elements). Elements are separated by commas. Within JSON-LD, array order is not preserved by default, unless
- specific markup is provided (see <a href="#lists">Lists</a>). This is because the basic data model of JSON-LD
- is a directed <tref>graph</tref>, which is inherently unordered.
- </dd>
- <dt><tdef>string</tdef></dt><dd>
- A string is a sequence of zero or more Unicode characters, wrapped in double quotes, using backslash escapes. A
- character is represented as a single character string.
- </dd>
- <dt><tdef>number</tdef></dt>
- <dd>
- A number is is similar to that used in most programming languages, except that the octal and hexadecimal formats are not used and that leading zeros are not allowed.</dd>
- <dt><tdef>true</tdef> and <tdef>false</tdef></dt><dd>
- Boolean values.
- </dd>
- <dt><tdef>null</tdef></dt><dd>
- The use of the <em>null</em> value is undefined within JSON-LD.
- <div class="issue">Supporting <em>null</em> in JSON-LD might have a number of advantages and should be evaluated. This is currently an <a href="https://github.com/json-ld/json-ld.org/issues/11">open issue</a>.</div>
- </dd>
- </dl>
-</p>
-</section>
-
-<section>
-<h2>Contributing</h2>
-
-<p>There are a number of ways that one may participate in the development of
-this specification:</p>
-
-<ul>
-<li>Technical discussion typically occurs on the public mailing list:
-<a href="http://lists.w3.org/Archives/Public/public-linked-json/">public-linked-json@w3.org</a>
-</li>
-
-<li><a href="http://json-ld.org/minutes/">Public teleconferences</a> are held
-on Tuesdays at 1500UTC on the second and fourth week of each month.
-</li>
-
-<li>Specification bugs and issues should be reported in the
-<a href="https://github.com/json-ld/json-ld.org/issues">issue tracker</a>.</li>
-
-<li><a href="https://github.com/json-ld/json-ld.org/tree/master/spec">Source code</a> for the
-specification can be found on Github.</li>
-
-<li>The <a href="http://webchat.freenode.net/?channels=#json-ld">#json-ld</a>
-IRC channel is available for real-time discussion on irc.freenode.net.</li>
-</ul>
-
-</section>
-
-</section>
-
-<section>
-<h1>Design</h1>
-
-<p>The following section outlines the design goals and rationale behind the
-JSON-LD markup language.
-</p>
-
-<section>
-<h2>Goals and Rationale</h2>
-
-<p>
-A number of design considerations were explored during the creation of this
-markup language:
-</p>
-
-<dl>
- <dt>Simplicity</dt>
- <dd>Developers need only know JSON and three keywords to use the basic
- functionality in JSON-LD. No extra processors or software libraries are
- necessary to use JSON-LD in its most basic form. The language attempts to
- ensure that developers have an easy learning curve.</dd>
- <dt>Compatibility</dt>
- <dd>The JSON-LD markup must be 100% compatible with JSON. This ensures that
- all of the standard JSON libraries work seamlessly with JSON-LD documents.</dd>
- <dt>Expressiveness</dt>
- <dd>The syntax must be able to express directed graphs, which have been proven
- to be able to simply express almost every real world data model.</dd>
- <dt>Terseness</dt>
- <dd>The JSON-LD syntax must be very terse and human readable, requiring as
- little as possible effort from the developer.</dd>
- <!--<dt>Pragmatism</dt>
- <dd>Mixing the expression of pure Linked Data with data that is not
- linked was an approach that was driven by pragmatism. JSON-LD attempts to be
- more practical than theoretical in its approach to Linked Data.</dd>-->
- <dt>Zero Edits, most of the time</dt>
- <dd>JSON-LD provides a mechanism that allows developers to specify
- context in a way that is out-of-band. This allows organizations that have
- already deployed large JSON-based infrastructure to add meaning to their
- JSON documents in a way that is not disruptive to their day-to-day operations and is
- transparent to their current customers. At times, mapping JSON to
- a graph representation can become difficult. In these instances, rather than
- having JSON-LD support esoteric markup, we chose not to support the use case
- and support a simplified syntax instead. So, while Zero Edits is a goal,
- it is not always possible without adding great complexity to the language.
- </dd>
- <dt>One-pass Conversion to RDF</dt>
- <dd>JSON-LD supports one-pass conversion to RDF with a very small memory footprint.</dd>
-</dl>
-</section>
-
-<section>
-<h2>Linked Data</h2>
-<p>
-The following definition for <tref>Linked Data</tref> is the one that will
-be used for this specification.
-</p>
-<ol>
- <li><tdef>Linked Data</tdef> is a set of documents, each containing a representation of a linked data graph.</li>
- <li>A <tdef>linked data graph</tdef> is an unordered labeled directed graph, where nodes are <tref>subject</tref>s or <tref>object</tref>s, and edges are properties.</li>
- <li>A <tdef>subject</tdef> is any node in a <tref>linked data graph</tref> with at least one outgoing edge.</li>
- <li>A <tref>subject</tref> SHOULD be labeled with an <tref>IRI</tref> (an Internationalized Resource Identifier as described in [[!RFC3987]]).</li>
- <li>An <tdef>object</tdef> is a node in a <tref>linked data graph</tref> with at least one incoming edge.</li>
- <li>An <tref>object</tref> MAY be labeled with an <tref>IRI</tref>.</li>
- <li>An object MAY be a <tdef>subject</tdef> and <tref>object</tref> at the same time.</li>
- <li>A <tdef>property</tdef> is an edge of the <tref>linked data graph</tref>.</li>
- <li>A <tref>property</tref> SHOULD be labeled with an <tref>IRI</tref>.</li>
- <li>An <tref>IRI</tref> that is a label in a <tref>linked data graph</tref> SHOULD be dereferencable to a <tref>Linked Data</tref> document describing the labeled <tref>subject</tref>, <tref>object</tref> or <tref>property</tref>.</li>
- <li>A <tdef>literal</tdef> is an <tref>object</tref> with a label that is not an <tref>IRI</tref></li>
-</ol>
-
-<p>
-Note that the definition for <tref>Linked Data</tref> above is silent on the
-topic of unlabeled nodes. Unlabeled nodes are not considered
-<tref>Linked Data</tref>. However, this specification allows for the expression
-of unlabled nodes, as most graph-based data sets on the Web contain a number
-of associated nodes that are not named and thus are not directly
-de-referenceable.
-</p>
-</section>
-
-<section>
-<h2>Linking Data</h2>
-
-<p>
-An Internationalized Resource Identifier
-(<tdef><abbr title="Internationalized Resource Identifier">IRI</abbr></tdef>),
-as described in [[!RFC3987]], is a mechanism for representing unique
-identifiers on the web. In <tref>Linked Data</tref>, an IRI is commonly
-used for expressing a <tref>subject</tref>, a <tref>property</tref> or an
-<tref>object</tref>.
-</p>
-
-<p>JSON-LD defines a mechanism to map JSON terms, i.e., keys and values, to IRIs. This does not mean
-that JSON-LD requires every key or value to be an IRI, but rather ensures that
-keys and values can be mapped to IRIs if the developer desires to transform
-their data into Linked Data. There are a few techniques that can ensure
-that developers will generate good Linked Data for the Web. JSON-LD
-formalizes those techniques.
-</p>
-
-<p>We will be using the following JSON markup as the example for the
-rest of this section:
-</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "name": "Manu Sporny",
- "homepage": "http://manu.sporny.org/",
- "avatar": "http://twitter.com/account/profile_image/manusporny"
-}
--->
-</pre>
-</section>
-
-<section>
-<h3>The Context</h3>
-
-<p>In JSON-LD, a context is used to map <tref>term</tref>s, i.e., keys and values
- in an JSON document, to
- <tref>IRI</tref>s. A <tdef>term</tdef> is a short word that MAY be expanded
-to an <tref>IRI</tref>. The Web uses IRIs for unambiguous identification. The
-idea is that these <tref>term</tref>s mean something that may be of use to
-other developers and that it is useful to give them an unambiguous identifier.
-That is, it is useful for <tref>term</tref>s to expand to IRIs so that
-developers don't accidentally step on each other's Web Vocabulary terms.
-For example, the term <code>name</code> may map directly to the IRI
-<code>http://xmlns.com/foaf/0.1/name</code>. This allows JSON-LD documents to
-be constructed using the common JSON practice of simple name/value pairs while
-ensuring that the data is useful outside of the page, API or database in which it
-resides.
-</p>
-
-<p>These Linked Data <tref>term</tref>s are typically collected in a context document that would look something like this:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "name": "http://xmlns.com/foaf/0.1/name",
- "homepage": "http://xmlns.com/foaf/0.1/homepage",
- "avatar": "http://xmlns.com/foaf/0.1/avatar"
-}
--->
-</pre>
-
-<p>This context document can then be used in an JSON-LD document by adding a single line. The JSON markup as shown in the previous section could be changed as follows to link to the context document:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- ****"@context": "http://example.org/json-ld-contexts/person",****
- "name": "Manu Sporny",
- "homepage": "http://manu.sporny.org/",
- "avatar": "http://twitter.com/account/profile_image/manusporny"
-}
--->
-</pre>
-
-<p>The addition above transforms the previous JSON document into a JSON document
-with added semantics because the <code>@context</code> specifies how the
-<strong>name</strong>, <strong>homepage</strong>, and <strong>avatar</strong>
-terms map to IRIs.
-Mapping those keys to IRIs gives the data global context. If two
-developers use the same IRI to describe a property, they are more than likely
-expressing the same concept. This allows both developers to re-use each others
-data without having to agree to how their data will inter-operate on a
-site-by-site basis. Contexts may also contain datatype information
-for certain <tref>term</tref>s as well as other processing instructions for
-the JSON-LD processor.</p>
-<p>Contexts may be specified in-line. This ensures that JSON-LD documents
-can be processed when a JSON-LD processor does not have access to the Web.</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- ****"@context": {
- "name": "http://xmlns.com/foaf/0.1/name",
- "homepage": "http://xmlns.com/foaf/0.1/homepage",
- "avatar": "http://xmlns.com/foaf/0.1/avatar"
- },****
- "name": "Manu Sporny",
- "homepage": "http://manu.sporny.org/",
- "avatar": "http://twitter.com/account/profile_image/manusporny"
-}
--->
-</pre>
-
-<p>JSON-LD strives to ensure that developers don't have to change the JSON
- that is going into and being returned from their Web APIs. This means
- that developers can also specify a context for JSON data in an out-of-band
- fashion. This is described later in this document. </p>
-
-<p>
- JSON-LD uses a special type of machine-readable document called a
- <tdef>Web Vocabulary</tdef> to define <tref>term</tref>s that are then used
- to describe concepts and "things" in the world.
- Typically, these Web Vocabulary documents have <tref>prefix</tref>es associated
- with them and contain a number of <tref>term</tref> declarations. A
- <tdef>prefix</tdef>, like a <tref>term</tref>, is a short word that expands
- to a Web Vocabulary base IRI. <tref>Prefix</tref>es are helpful when a developer
- wants to mix multiple vocabularies together in a context, but does not want
- to go to the trouble of defining every single term in every single vocabulary.
- Some Web Vocabularies may have dozens of terms defined. If a developer wants to use
- 3-4 different vocabularies, the number of terms that
- would have to be declared in a single context could become quite large. To
- reduce the number of different terms that must be defined, JSON-LD also allows
- prefixes to be used to compact IRIs.
-<p>
-
-<p>For example, the IRI <code>http://xmlns.com/foaf/0.1/</code>
-specifies a <tref>Web Vocabulary</tref> which may be represented using the
-<code>foaf</code> <tref>prefix</tref>. The <code>foaf</code> Web Vocabulary
-contains a term called <strong>name</strong>. If you join the
-<code>foaf</code> <tref>prefix</tref> with the <strong>name</strong> suffix,
-you can build a compact IRI that will expand out into an absolute IRI for the
-<code>http://xmlns.com/foaf/0.1/name</code> vocabulary term.
-That is, the compact IRI, or short-form, is <code>foaf:name</code> and the
-expanded-form is <code>http://xmlns.com/foaf/0.1/name</code>. This vocabulary
-term is used to specify a person's name.
-</p>
-
-<p>Developers, and machines, are able to use this IRI (plugging it
-directly into a web browser, for instance) to go to the term and get a
-definition of what the term means. Much like we can use <a href="http://wordnet.princeton.edu/">WordNet</a> today to
-see the definition
-of words in the English language. Developers and machines need the same sort of
-definition of terms. IRIs provide a way to ensure that these terms
-are unambiguous.
-</p>
-
-<p>The context provides a collection of vocabulary <tref>term</tref>s and
-<tref>prefix</tref>es that can be used to expand JSON keys and values into
-<tref>IRI</tref>s.</p>
-
-<p class="note">To ensure the best possible performance, it is a best practice to
-put the context definition at the top of the JSON-LD document. If it isn't listed
-first, processors have to save each key-value pair until the context is processed.
-This creates a memory and complexity burden for one-pass processors.</p>
-
-</section>
-
-<section>
-<h3>From JSON to JSON-LD</h3>
-
-<p>If a set of terms such as, <strong>name</strong>, <strong>homepage</strong>,
-and <strong>avatar</strong>,
-are defined in a context, and that context is used to resolve the
-names in JSON objects, machines are able to automatically expand the terms to
-something meaningful and unambiguous, like this:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "****http://xmlns.com/foaf/0.1/name****": "Manu Sporny",
- "****http://xmlns.com/foaf/0.1/homepage****": "http://manu.sporny.org"
- "****http://rdfs.org/sioc/ns#avatar****": "http://twitter.com/account/profile_image/manusporny"
-}
- -->
-</pre>
-
-<p>Doing this allows JSON to be unambiguously machine-readable without
-requiring developers to drastically change their workflow.</p>
-<p class="note">Please note that this JSON-LD document doesn't define the
-subject and will thus result in an unlabeled or blank node.</p>
-
-</section>
-
-</section>
-
-</section>
-
-<section>
-<h1>Basic Concepts</h1>
-
-<p>JSON-LD is designed to ensure that Linked Data concepts can be marked
-up in a way that is simple to understand and author by Web developers. In many
-cases, regular JSON markup can become Linked Data with the simple addition
-of a context. As more JSON-LD features are used, more semantics are added
-to the JSON markup.</p>
-
-<section>
-<h2>IRIs</h2>
-
-<p>Expressing IRIs are fundamental to Linked Data as that is how most
-<tref>subject</tref>s and many <tref>object</tref> are named. IRIs can be
-expressed in a variety of different ways in JSON-LD.</p>
-
-<ol>
- <li>In general, <tref>term</tref>s in the key position in
- a <tref>JSON object</tref> that have a mapping to an IRI or another key in the context are
- expanded to an IRI by JSON-LD processors. There are special rules for
- processing keys in <code>@context</code> and when dealing with keys that
- start with the <code>@subject</code> character.</li>
- <li>An IRI is generated for the value specified using <code>@subject</code>,
- if it is a <tref>string</tref>.</li>
- <li>An IRI is generated for the value specified using <code>@type</code>.</li>
- <li>An IRI is generated for the value specified using the <code>@iri</code>
- keyword.</li>
- <li>An IRI is generated when there are <code>@coerce</code> rules in
- effect for a key named <code>@iri</code>.</li>
-</ol>
-
-<p>IRIs can be expressed directly in the key position like so:
-</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
-...
- "****http://xmlns.com/foaf/0.1/name****": "Manu Sporny",
-...
-}
--->
-</pre>
-
-<p>In the example above, the key
-<code>http://xmlns.com/foaf/0.1/name</code> is interpreted as an IRI, as
-opposed to being interpreted as a string.</p>
-
-<p>Term expansion occurs for IRIs if a term is defined within the
-<tref>active context</tref>:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "****@context****": {"****name****": "****http://xmlns.com/foaf/0.1/name****"},
-...
- "****name****": "Manu Sporny",
-...
-}
--->
-</pre>
-
-<p><tref>Prefix</tref>es are expanded when used in keys:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "****@context****": {"****foaf****": "****http://xmlns.com/foaf/0.1/****"},
-...
- "****foaf:name****": "Manu Sporny",
-...
-}
--->
-</pre>
-
-<p><code>foaf:name</code> above will automatically expand out to the IRI
-<code>http://xmlns.com/foaf/0.1/name</code>.</p>
-
-<p>An IRI is generated when a value is associated with a key using
-the <code>@iri</code> keyword:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
-...
- "homepage": { "****@iri****": "http://manu.sporny.org" }
-...
-}
--->
-</pre>
-
-<p>If type coercion rules are specified in the <code>@context</code> for
-a particular vocabulary term, an IRI is generated:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{****
- "@context":
- {
- ...
- "@coerce":
- {
- "@iri": "homepage"
- }
- }****
-...
- "homepage": "http://manu.sporny.org/",
-...
-}
--->
-</pre>
-
-<p>Even though the value <code>http://manu.sporny.org/</code> is a <tref>string</tref>,
-the type coercion rules will transform the value into an IRI when processed
-by a JSON-LD Processor</p>
-
-</section>
-
-<section>
-<h2>Identifying the Subject</h2>
-
-<p>
- To be able to externally reference nodes, it is important that each node has an unambiguous identifier.
- <tref>IRI</tref>s are a fundamental concept of Linked Data, and nodes should have a de-referencable
- identifier used to name and locate them. For nodes to be truely linked, de-referencing the identifier
- should result in a representation of that node. Associating an IRI with a node tells an application
- that the returned document contains a description of the node requested.
-</p>
-<p>
- JSON-LD documents may also contain descriptions of other nodes, so it is necessary to be able to
- uniquely identify each node which may be externally referenced.
-</p>
-<p>A <tref>subject</tref>
- of an object in JSON is declared using the <code>@subject</code> key. The subject is the
-first piece of information needed by the JSON-LD processor in order to
-create the (subject, property, object) tuple, also known as a triple.</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
-...
- "****@subject****": "****http://example.org/people#joebob****",
-...
-}
--->
-</pre>
-
-<p>The example above would set the subject to the IRI
-<code>http://example.org/people#joebob</code>.
-</p>
-
-<p class="note">To ensure the best possible performance, it is a best practice to
-put the <code>@subject</code> key before other key-value pairs in an object. If
-it isn't listed first, processors have to save each key-value pair until
-<code>@subject</code> is processed before they can create valid triples. This
-creates a memory and complexity burden for one-pass processors.</p>
-
-</section>
-
-<section>
-<h2>Specifying the Type</h2>
-
-<p>The type of a particular subject can be specified using the
-<code>@type</code> key. Specifying the type in this way will generate a
-triple of the form (subject, type, type-iri).</p>
-
-<p>To be Linked Data, types MUST be uniquely identified by an
- <tref>IRI</tref>.</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
-...
- "@subject": "http://example.org/people#joebob",
- "****@type****": "****http://xmlns.com/foaf/0.1/Person****",
-...
-}
--->
-</pre>
-
-<p>The example above would generate the following triple if the JSON-LD
-document is mapped to RDF (in N-Triples notation):</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-<http://example.org/people#joebob>
- <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
- <http://xmlns.com/foaf/0.1/Person> .
--->
-</pre>
-
-</section>
-
-<section>
-<h2>Strings</h2>
-
-<p>Regular text strings, also referred to as <tdef>plain literal</tdef>s, are
-easily expressed using regular JSON <tref>string</tref>s.</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
-...
- "name": "****Mark Birbeck****",
-...
-}
- -->
-</pre>
-
-</section>
-
-<section>
-<h2>String Internationalization</h2>
-
-<p>JSON-LD makes an assumption that strings with associated language encoding
-information are not very common when used in JavaScript and Web Services.
-Thus, it takes a little more effort to express strings with associated
-language information.</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
-...
- "name": ****
- {
- "@literal": "花澄",
- "@language": "ja"
- }****
-...
-}
--->
-</pre>
-
-<p>The example above would generate a <tref>plain literal</tref> for
-<em>花澄</em> and associate the <code>ja</code> language code with the triple
-that is generated. Languages MUST be expressed in [[!BCP47]] format.</p>
-
-</section>
-
-<section>
-<h2>Datatypes</h2>
-
-<p>
- A value with an associated datatype, also known as a
- <tdef>typed literal</tdef>, is indicated by associating a literal with
- an IRI which indicates the literal's datatype. Typed literals may be
- expressed in JSON-LD in three ways:
-</p>
-
-<ol>
- <li>By utilizing the <code>@coerce</code> keyword.</li>
- <li>By utilizing the expanded form for specifying objects.</li>
- <li>By using a native JSON datatype.</li>
-</ol>
-
-<p>The first example uses the <code>@coerce</code> keyword to express a
-typed literal:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{****
- "@context":
- {
- "modified": "http://purl.org/dc/terms/modified",
- "dateTime": "http://www.w3.org/2001/XMLSchema#dateTime"
- "@coerce":
- {
- "dateTime": "modified"
- }
- }****
-...
- "modified": "2010-05-29T14:17:39+02:00",
-...
-}
--->
-</pre>
-
-<p>The second example uses the expanded form for specifying objects:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
-...
- "modified": ****
- {
- "@literal": "2010-05-29T14:17:39+02:00",
- "@datatype": "dateTime"
- }****
-...
-}
--->
-</pre>
-
-<p>Both examples above would generate an object with the literal value of
-<code>2010-05-29T14:17:39+02:00</code> and the datatype of
-<code>http://www.w3.org/2001/XMLSchema#dateTime</code>.</p>
-
-<p>The third example uses a built-in native JSON type, a
- <tref>number</tref>, to express a datatype:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
-...
- "@subject": "http://example.org/people#joebob",
- "age": ****31****
-...
-}
--->
-</pre>
-
-<p>The example above would generate the following triple:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-<http://example.org/people#joebob>
- <http://xmlns.com/foaf/0.1/age>
- "31"^^<http://www.w3.org/2001/XMLSchema#integer> .
--->
-</pre>
-
-</section>
-
-<section>
-<h2>Multiple Objects for a Single Property</h2>
-
-<p>A JSON-LD author can express multiple triples in a compact way by using
-<tref>array</tref>s. If a subject has multiple values for the same property, the author
-MAY express each property as an <tref>array</tref>.</p>
-
-<p class="note">In JSON-LD, multiple objects on a property are not ordered. This is because typically graphs
-are not inherently ordered data structures. To see more on creating ordered collections
-in JSON-LD, see <a href="#lists">Lists</a>.
-</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
-...
- "@subject": "http://example.org/people#joebob",
- "nick": ****["joe", "bob", "jaybee"]****,
-...
-}
--->
-</pre>
-
-<p>The markup shown above would generate the following triples:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-<http://example.org/people#joebob>
- <http://xmlns.com/foaf/0.1/nick>
- "joe" .
-<http://example.org/people#joebob>
- <http://xmlns.com/foaf/0.1/nick>
- "bob" .
-<http://example.org/people#joebob>
- <http://xmlns.com/foaf/0.1/nick>
- "jaybee" .
--->
-</pre>
-
-</section>
-
-<section>
-<h2>Multiple Typed Literals for a Single Property</h2>
-
-<p>Multiple <tref>typed literal</tref>s may also be expressed using the expanded
-form for objects:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
-...
- "@subject": "http://example.org/articles/8",
- "modified": ****
- [
- {
- "@literal": "2010-05-29T14:17:39+02:00",
- "@datatype": "dateTime"
- },
- {
- "@literal": "2010-05-30T09:21:28-04:00",
- "@datatype": "dateTime"
- }
- ]****
-...
-}
--->
-</pre>
-
-<p>The markup shown above would generate the following triples:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-<http://example.org/articles/8>
- <http://purl.org/dc/terms/modified>
- "2010-05-29T14:17:39+02:00"^^http://www.w3.org/2001/XMLSchema#dateTime .
-<http://example.org/articles/8>
- <http://purl.org/dc/terms/modified>
- "2010-05-30T09:21:28-04:00"^^http://www.w3.org/2001/XMLSchema#dateTime .
--->
-</pre>
-
-</section>
-
-<section>
-<h2>Expansion</h2>
-
-<p>Expansion is the process of taking a JSON-LD document and applying a
-context such that all IRI, datatypes, and literal values are expanded so
-that the context is no longer necessary. JSON-LD document expansion
-is typically used as a part of <a href="#normalization">Framing</a> or
-<a href="#normalization">Normalization</a>.</p>
-
-<p>For example, assume the following JSON-LD input document:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "@context":
- {
- "name": "http://xmlns.com/foaf/0.1/name",
- "homepage": "http://xmlns.com/foaf/0.1/homepage",
- "@coerce":
- {
- "@iri": "homepage"
- }
- },
- "name": "Manu Sporny",
- "homepage": "http://manu.sporny.org/"
-}
--->
-</pre>
-
-<p>Running the JSON-LD Expansion algorithm against the JSON-LD input document
-provided above would result in the following output:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "http://xmlns.com/foaf/0.1/name": "Manu Sporny",
- "http://xmlns.com/foaf/0.1/homepage":
- {
- "@iri": "http://manu.sporny.org/"
- }
-}
--->
-</pre>
-
-</section>
-
-<section>
-<h2>Compaction</h2>
-
-<p>Compaction is the process of taking a JSON-LD document and applying a
-context such that the most compact form of the document is generated. JSON
-is typically expressed in a very compact, key-value format. That is, full
-IRIs are rarely used as keys. At times, a JSON-LD document may be received
-that is not in its most compact form. JSON-LD, via the API, provides a way
-to compact a JSON-LD document.
-</p>
-
-<p>For example, assume the following JSON-LD input document:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "http://xmlns.com/foaf/0.1/name": "Manu Sporny",
- "http://xmlns.com/foaf/0.1/homepage":
- {
- "@iri": "http://manu.sporny.org/"
- }
-}
--->
-</pre>
-
-<p>Additionally, assume the following developer-supplied JSON-LD context:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "name": "http://xmlns.com/foaf/0.1/name",
- "homepage": "http://xmlns.com/foaf/0.1/homepage",
- "@coerce":
- {
- "@iri": "homepage"
- }
-}
--->
-</pre>
-
-<p>Running the JSON-LD Compaction algorithm given the context supplied above
-against the JSON-LD input document provided above would result in the following
-output:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "@context":
- {
- "name": "http://xmlns.com/foaf/0.1/name",
- "homepage": "http://xmlns.com/foaf/0.1/homepage",
- "@coerce":
- {
- "@iri": "homepage"
- }
- },
- "name": "Manu Sporny",
- "homepage": "http://manu.sporny.org/"
-}
--->
-</pre>
-
-<p>The compaction algorithm also enables the developer to map any expanded
-format into an application-specific compacted format. While the context
-provided above mapped <code>http://xmlns.com/foaf/0.1/name</code> to
-<strong>name</strong>, it could have also mapped it to any arbitrary string
-provided by the developer.
-</p>
-
-</section>
-
-<section>
-<h2>Framing</h2>
-
-<p>A JSON-LD document is a representation of a directed graph. A single
-directed graph can have many different serializations, each expressing
-exactly the same information. Developers typically work with trees, represented as
-<tref>JSON object</tref>s. While mapping a graph to
-a tree can be done, the layout of the end result must be specified in advance.
-A <tdef>Frame</tdef> can be used by a developer on a JSON-LD document to
-specify a deterministic layout for a graph.
-</p>
-
-<p>Framing is the process of taking a JSON-LD document, which expresses a
-graph of information, and applying a specific graph layout
-(called a <tref>Frame</tref>).
-</p>
-
-<p>The JSON-LD document below expresses a library, a book and a chapter:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "@context": {
- "Book": "http://example.org/vocab#Book",
- "Chapter": "http://example.org/vocab#Chapter",
- "contains": "http://example.org/vocab#contains",
- "creator": "http://purl.org/dc/terms/creator"
- "description": "http://purl.org/dc/terms/description"
- "Library": "http://example.org/vocab#Library",
- "title": "http://purl.org/dc/terms/title",
- "@coerce":
- {
- "@iri": "contains"
- },
- },
- "@subject":
- [{
- "@subject": "http://example.com/library",
- "@type": "Library",
- "contains": "http://example.org/library/the-republic"
- },
- {
- "@subject": "http://example.org/library/the-republic",
- "@type": "Book",
- "creator": "Plato",
- "title": "The Republic",
- "contains": "http://example.org/library/the-republic#introduction"
- },
- {
- "@subject": "http://example.org/library/the-republic#introduction",
- "@type": "Chapter",
- "description": "An introductory chapter on The Republic.",
- "title": "The Introduction"
- }]
-}-->
-</pre>
-
-<p>Developers typically like to operate on items in a hierarchical, tree-based
-fashion. Ideally, a developer would want the data above sorted into top-level
-libraries, then the books that are contained in each library, and then the
-chapters contained in each book. To achieve that layout, the developer can
-define the following <tref>frame</tref>:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "@context": {
- "Book": "http://example.org/vocab#Book",
- "Chapter": "http://example.org/vocab#Chapter",
- "contains": "http://example.org/vocab#contains",
- "creator": "http://purl.org/dc/terms/creator"
- "description": "http://purl.org/dc/terms/description"
- "Library": "http://example.org/vocab#Library",
- "title": "http://purl.org/dc/terms/title"
- },
- "@type": "Library",
- "contains": {
- "@type": "Book",
- "contains": {
- "@type": "Chapter"
- }
- }
-}
--->
-</pre>
-
-<p>When the framing algorithm is run against the previously defined
-JSON-LD document, paired with the <tref>frame</tref> above, the following
-JSON-LD document is the end result:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "@context": {
- "Book": "http://example.org/vocab#Book",
- "Chapter": "http://example.org/vocab#Chapter",
- "contains": "http://example.org/vocab#contains",
- "creator": "http://purl.org/dc/terms/creator"
- "description": "http://purl.org/dc/terms/description"
- "Library": "http://example.org/vocab#Library",
- "title": "http://purl.org/dc/terms/title"
- },
- "@subject": "http://example.org/library",
- "@type": "Library",
- "contains": {
- ****"@subject": "http://example.org/library/the-republic",****
- "@type": "Book",
- ****"creator": "Plato",****
- ****"title": "The Republic",****
- "contains": {
- ****"@subject": "http://example.org/library/the-republic#introduction",****
- "@type": "Chapter",
- ****"description": "An introductory chapter on The Republic.",****
- ****"title": "The Introduction"****
- },
- },
-}
--->
-</pre>
-
-<p>The JSON-LD framing algorithm allows developers to query by example and
-force a specific tree layout to a JSON-LD document.
-</p>
-
-</section>
-
-</section>
-
-<section>
-<h1>Advanced Concepts</h1>
-
-<p>JSON-LD has a number of features that provide functionality above and beyond
-the core functionality described above. The following sections outline the
-features that are specific to JSON-LD.
-</p>
-
-<section>
- <h2>Vocabulary Prefixes</h2>
- <p>
- Vocabulary terms in Linked Data documents may draw from a number of
- different Web vocabularies. At times, declaring every single term that
- a document uses can require the developer to declare tens, if not
- hundreds of potential vocabulary terms that may be used across an
- application. This is a concern for at least three reasons; the
- first is the cognitive load on the developer, the second is
- the serialized size of the context, the third is future-proofing
- application contexts. In order to address these issues, the concept of a
- <tref>prefix</tref> mechanism is introduced.</p>
- <p>
- A <tdef>prefix</tdef> is a compact way of expressing a base
- <tref>IRI</tref> to a <tref>Web Vocabulary</tref>.
- Generally, these prefixes are used by concatenating the <em>prefix</em> and
- a <em>term</em> separated by a colon (<code>:</code>).
- The prefix is a short string that identifies a particular Web vocabulary.
- For example, the prefix <code>foaf</code> may be used as a short
- hand for the Friend-of-a-Friend Web Vocabulary, which is identified using
- the IRI <code>http://xmlns.com/foaf/0.1/</code>. A developer may append any of
- the FOAF Vocabulary terms to the end of the prefix to specify a short-hand
- version of the full IRI for the vocabulary term. For example,
- <code>foaf:name</code> would be expanded out to the IRI
- <code>http://xmlns.com/foaf/0.1/name</code>. Instead of having to remember
- and type out the entire IRI, the developer can instead use the prefix in
- their JSON-LD markup.
- </p>
- <p>
- The ability to use <tref>prefix</tref>es reduces the need for developers
- to declare every vocabulary term that they intend to use in
- the JSON-LD context. This reduces document serialization size because
- every vocabulary term need not be declared in the context.
- <tref>Prefix</tref> also
- reduce the cognitive load on the developer. It is far easier to
- remember <code>foaf:name</code> than it is to remember
- <code>http://xmlns.com/foaf/0.1/name</code>. The use of prefixes also
- ensures that a context document does not have to be updated in lock-step
- with an externally defined <tref>Web Vocabulary</tref>. Without prefixes, a developer
- would need to keep their application context terms in lock-step with an
- externally defined Web Vocabulary. Rather, by just declaring the
- Web Vocabulary prefix, one can use new terms as they're declared
- without having to update the application's JSON-LD context.
- </p>
- <p>Consider the following example:</p>
- <pre class="example" data-transform="updateExample">
-<!--
-{
- "@context": {
- ****"dc": "http://purl.org/dc/elements/1.1/",****
- ****"ex": "http://example.org/vocab#"****
- },
- "@subject": "http://example.org/library",
- "@type": ****"ex:Library"****,
- ****"ex:contains"****: {
- "@subject": "http://example.org/library/the-republic",
- "@type": ****"ex:Book"****,
- ****"dc:creator"****: "Plato",
- ****"dc:title"****: "The Republic",
- ****"ex:contains"****: {
- "@subject": "http://example.org/library/the-republic#introduction",
- "@type": ****"ex:Chapter"****,
- ****"dc:description"****: "An introductory chapter on The Republic.",
- ****"dc:title"****: "The Introduction"
- },
- },
-}
--->
- </pre>
- <p>
- In this example, two different vocabularies are referred to using
- prefixes. Those prefixes are then used as type and property values using
- the <code>prefix:term</code> notation.
- </p>
- <p>
- Prefixes, also known as CURIEs, are defined more formally in RDFa Core 1.1,
- <cite><a href="http://www.w3.org/TR/rdfa-core/#s_curies">Section 6
- "CURIE Syntax Definition"</a></cite> [[RDFA-CORE]].
- JSON-LD does not support the square-bracketed CURIE syntax as the
- mechanism is not required to disambiguate IRIs in a JSON-LD document like
- it is in HTML documents.
- </p>
-</section>
-
-<section>
-<h2>Automatic Typing</h2>
-
-<p>Since JSON is capable of expressing typed information such as doubles,
-integers, and boolean values. As demonstrated below, JSON-LD utilizes that
-information to create <tref>typed literal</tref>s:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
-...
- // The following two values are automatically converted to a type of xsd:double
- // and both values are equivalent to each other.
- "measure:cups": ****5.3****,
- "measure:cups": ****5.3e0****,
- // The following value is automatically converted to a type of xsd:double as well
- "space:astronomicUnits": ****6.5e73****,
- // The following value should never be converted to a language-native type
- "measure:stones": ****{ "@literal": "4.8", "@datatype": "xsd:decimal" }****,
- // This value is automatically converted to having a type of xsd:integer
- "chem:protons": ****12****,
- // This value is automatically converted to having a type of xsd:boolean
- "sensor:active": ****true****,
-...
-}
--->
-</pre>
-
-<p class="note">When dealing with a number of modern programming languages,
-including JavaScript ECMA-262, there is no distinction between
-<strong>xsd:decimal</strong> and <strong>xsd:double</strong> values. That is,
-the <tref>number</tref> <code>5.3</code> and the <tref>number</tref>
-<code>5.3e0</code> are treated as if they were the same. When converting from
-JSON-LD to a language-native format and back, datatype information is lost in a
-number of these languages. Thus, one could say that <code>5.3</code> is a
-<strong>xsd:decimal</strong> and <code>5.3e0</code> is an
-<strong>xsd:double</strong> in JSON-LD, but when both values are
-converted to a language-native format the datatype difference between the two
-is lost because the machine-level representation will almost always be a
-<strong>double</strong>.
-Implementers should be aware of this potential round-tripping issue between
-<strong>xsd:decimal</strong> and <strong>xsd:double</strong>. Specifically
-objects with a datatype of <strong>xsd:decimal</strong> MUST NOT be converted
-to a language native type.
-</p>
-
-</section>
-
-<section>
-<h2>Type Coercion</h2>
-
-<p>JSON-LD supports the coercion of values to particular data types.
-Type coercion allows someone deploying JSON-LD to coerce the incoming or
-outgoing types to the proper data type based on a mapping of data type IRIs to
-property types. Using type coercion, one may convert simple JSON data to
-properly typed RDF data.</p>
-
-<p>The example below demonstrates how a JSON-LD author can coerce values to
-<tref>plain literal</tref>s, <tref>typed literal</tref>s and IRIs.</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "@context":
- {
- "rdf": "http://www.w3.org/1999/02/22-rdf-syntax-ns#",
- "xsd": "http://www.w3.org/2001/XMLSchema#",
- "name": "http://xmlns.com/foaf/0.1/name",
- "age": "http://xmlns.com/foaf/0.1/age",
- "homepage": "http://xmlns.com/foaf/0.1/homepage",
-**** "@coerce":
- {
- "xsd:integer": "age",
- "@iri": "homepage"
- }****
- },
- "name": "John Smith",
- "age": ****"41"****,
- "homepage": ****"http://example.org/home/"****
-}
--->
-</pre>
-
-<p>The example above would generate the following triples:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-_:bnode1
- <http://xmlns.com/foaf/0.1/name>
- "John Smith" .
-_:bnode1
- <http://xmlns.com/foaf/0.1/age>
- "41"^^http://www.w3.org/2001/XMLSchema#integer .
-_:bnode1
- <http://xmlns.com/foaf/0.1/homepage>
- <http://example.org/home/> .
--->
-</pre>
-
-</section>
-
-<section>
- <h2>Chaining</h2>
- <p>
- Object <tdef>chaining</tdef> is a JSON-LD feature that allows an author to
- use the definition of JSON-LD objects as <tref>property</tref> values. This
- is a commonly used mechanism for creating a parent-child relationship
- between two <tref>subject</tref>s.
- </p>
- <p>The example shows an two subjects related by a property from the first
- subject:</p>
-
- <pre class="example" data-transform="updateExample">
- <!--
- {
- ...
- "name": "Manu Sporny",
- "****knows****": {
- "****@type****": "****Person****",
- "****name****": "****Gregg Kellogg****",
- }
- ...
- }
- -->
- </pre>
-
- <p>
- An object definition, like the one used above, MAY be used as a
- JSON value at any point in JSON-LD.
- </p>
-</section>
-
-<section>
-<h2>Identifying Unlabeled Nodes</h2>
-
-<p>At times, it becomes necessary to be able to express information without
-being able to specify the subject. Typically, this type of node is called
-an unlabeled node or a blank node. In JSON-LD, unlabeled node identifiers are
-automatically created if a subject is not specified using the
-<code>@subject</code> keyword. However, authors may provide identifiers for
-unlabeled nodes by using the special <code>_</code> (underscore)
-<tref>prefix</tref>. This allows to reference the node locally within the
-document but not in an external document.</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
-...
- "@subject": "****_:foo****",
-...
-}
- -->
-</pre>
-
-<p>The example above would set the subject to <code>_:foo</code>, which can
-then be used later on in the JSON-LD markup to refer back to the
-unlabeled node. This practice, however, is usually frowned upon when
-generating Linked Data. If a developer finds that they refer to the unlabeled
-node more than once, they should consider naming the node using a resolve-able
-IRI.
-</p>
-
-</section>
-
-<section>
-<h2>Aliasing Keywords</h2>
-
-<p>JSON-LD allows all of the syntax keywords, except for <code>@context</code>,
-to be aliased. This feature allows more legacy JSON content to be supported
-by JSON-LD. It also allows developers to design domain-specific implementations
-using only the JSON-LD context.</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "@context":
- {
- ****"url": "@subject"****,
- ****"a": "@type"****,
- "name": "http://schema.org/name"
- },
- "url": "http://example.com/about#gregg",
- "a": "http://schema.org/Person",
- "name": "Gregg Kellogg"
-}
--->
-</pre>
-
-<p>In the example above, the <code>@subject</code> and <code>@type</code>
-keywords have been given the aliases <strong>url</strong> and
-<strong>a</strong>, respectively.
-</p>
-
-</section>
-
-<section>
-<h2>Normalization</h2>
-
-<p>Normalization is the process of taking <tref>JSON-LD input</tref> and
-performing a deterministic transformation on that input that results in a
-<tref>JSON-LD output</tref> that any conforming JSON-LD processor would have
-generated given the same input. The problem is a fairly difficult technical
-problem to solve because it requires a directed graph to be ordered into a
-set of nodes and edges in a deterministic way. This is easy to do when all of
-the nodes have unique names, but very difficult to do when some of the nodes
-are not labeled.
-</p>
-
-<p>Normalization is useful when comparing two graphs against one another,
-when generating a detailed list of differences between two graphs, and
-when generating a cryptographic digital signature for information contained
-in a graph or when generating a hash of the information contained in a graph.
-</p>
-
-<p>The example below is an un-normalized JSON-LD document:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "@context":
- {
- "name": "http://xmlns.com/foaf/0.1/name",
- "homepage": "http://xmlns.com/foaf/0.1/homepage",
- "xsd": "http://www.w3.org/2001/XMLSchema#",
- "@coerce":
- {
- "@iri": ["homepage"]
- }
- },
- "name": "Manu Sporny",
- "homepage": "http://manu.sporny.org/"
-}
--->
-</pre>
-
-<p>The example below is the normalized form of the JSON-LD document above:</p>
-
-<p class="note">Whitespace is used below to aid readability. The normalization
-algorithm for JSON-LD removes all unnecessary whitespace in the fully
-normalized form.</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-[{
- "@subject":
- {
- "@iri": "_:c14n0"
- },
- "http://xmlns.com/foaf/0.1/homepage":
- {
- "@iri": "http://manu.sporny.org/"
- },
- "http://xmlns.com/foaf/0.1/name": "Manu Sporny"
-}]
--->
-</pre>
-
-<p>Notice how all of the <tref>term</tref>s have been expanded and sorted in
-alphabetical order. Also, notice how the <tref>subject</tref> has been
-labeled with a <tref>blank node identifier</tref>. Normalization ensures that any arbitrary
-graph containing exactly the same information would be normalized to exactly
-the same form shown above.</p>
-
-</section>
-
-</section>
-
-<section>
-<h2>The Application Programming Interface</h2>
-
-<p>This API provides a clean mechanism that enables developers to convert
-JSON-LD data into a a variety of output formats that are easier to work with in
-various programming languages. If a JSON-LD API is provided in a programming
-environment, the entirety of the following API MUST be implemented.
-</p>
-
-<section>
-<h3>JsonLdProcessor</h3>
-<dl title="[NoInterfaceObject] interface JsonLdProcessor" class="idl">
-
- <dt>object expand()</dt>
- <dd><a href="#expansion">Expands</a> the given <code>input</code>
- according to the steps in the
- <a href="#expansion-algorithm">Expansion Algorithm</a>. The
- <code>input</code> MUST be copied, expanded and returned if there are
- no errors. If the expansion fails, an appropriate exception MUST be thrown.
-
- <dl class="parameters">
- <dt>object input</dt>
- <dd>The JSON-LD object to copy and perform the expansion upon.</dd>
- <dt>object optional? context</dt>
- <dd>An external context to use additionally to the context embedded in <code>input</code> when expanding the <code>input</code>.</dd>
- </dl>
-
- <dl class="exception" title="InvalidContext">
- <dt>INVALID_SYNTAX</dt>
- <dd>A general syntax error was detected in the <code>@context</code>.
- For example, if a <code>@coerce</code> key maps to anything other than
- a string or an array of strings, this exception would be raised.</dd>
- <dt>MULTIPLE_DATATYPES</dt>
- <dd>There is more than one target datatype specified for a single
- property in the list of coercion rules. This means that the processor
- does not know what the developer intended for the target datatype for a
- property.</dd>
- </dl>
-
- </dd>
-
- <dt>object compact()</dt>
- <dd><a href="#compaction">Compacts</a> the given <code>input</code>
- according to the steps in the
- <a href="#compaction-algorithm">Compaction Algorithm</a>. The
- <code>input</code> MUST be copied, compacted and returned if there are
- no errors. If the compaction fails, an appropirate exception MUST be
- thrown.
- <dl class="parameters">
- <dt>object input</dt>
- <dd>The JSON-LD object to perform compaction on.</dd>
- <dt>object optional? context</dt>
- <dd>The base context to use when compacting the <code>input</code>.</dd>
- </dl>
-
- <dl class="exception" title="InvalidContext">
- <dt>INVALID_SYNTAX</dt>
- <dd>A general syntax error was detected in the <code>@context</code>.
- For example, if a <code>@coerce</code> key maps to anything other than
- a string or an array of strings, this exception would be raised.</dd>
- <dt>MULTIPLE_DATATYPES</dt>
- <dd>There is more than one target datatype specified for a single
- property in the list of coercion rules. This means that the processor
- does not know what the developer intended for the target datatype for a
- property.</dd>
- </dl>
-
- <dl class="exception" title="ProcessingError">
- <dt>LOSSY_COMPACTION</dt>
- <dd>The compaction would lead to a loss of information, such as a
- <code>@language</code> value.</dd>
- <dt>CONFLICTING_DATATYPES</dt>
- <dd>The target datatype specified in the coercion rule and the
- datatype for the typed literal do not match.</dd>
- </dl>
-
- </dd>
-
- <dt>object frame()</dt>
- <dd><a href="#framing">Frames</a> the given <code>input</code>
- using the <code>frame</code> according to the steps in the
- <a href="#framing-algorithm">Framing Algorithm</a>. The
- <code>input</code> is used to build the framed output and is returned if
- there are no errors. If there are no matches for the frame,
- <code>null</code> MUST be returned. Exceptions MUST be thrown if there are
- errors.
- <dl class="parameters">
- <dt>object input</dt>
- <dd>The JSON-LD object to perform framing on.</dd>
- <dt>object frame</dt>
- <dd>The frame to use when re-arranging the data.</dd>
- <dt>object options</dt>
- <dd>A set of options that will affect the framing algorithm.</dd>
- </dl>
-
- <dl class="exception" title="InvalidFrame">
- <dt>INVALID_SYNTAX</dt>
- <dd>A frame must be either an object or an array of objects, if the frame
- is neither of these types, this exception is thrown.</dd>
- <dt>MULTIPLE_EMBEDS</dt>
- <dd>A subject IRI was specified in more than one place in the input
- frame. More than one embed of a given subject IRI is not allowed, and if
- requested, MUST result in this exception.</dd>
- </dl>
-
- </dd>
-
- <dt>object normalize()</dt>
- <dd><a href="#normalization">Normalizes</a> the given <code>input</code>
- according to the steps in the
- <a href="#normalization-algorithm">Normalization Algorithm</a>. The
- <code>input</code> MUST be copied, normalized and returned if there are
- no errors. If the compaction fails, <code>null</code> MUST be returned.
- <dl class="parameters">
- <dt>object input</dt>
- <dd>The JSON-LD object to perform normalization upon.</dd>
- <dt>object optional? context</dt>
- <dd>An external context to use additionally to the context embedded in <code>input</code> when expanding the <code>input</code>.</dd>
- </dl>
-
- <dl class="exception" title="InvalidContext">
- <dt>INVALID_SYNTAX</dt>
- <dd>A general syntax error was detected in the <code>@context</code>.
- For example, if a <code>@coerce</code> key maps to anything other than
- a string or an array of strings, this exception would be raised.</dd>
- <dt>MULTIPLE_DATATYPES</dt>
- <dd>There is more than one target datatype specified for a single
- property in the list of coercion rules. This means that the processor
- does not know what the developer intended for the target datatype for a
- property.</dd>
- </dl>
-
- </dd>
-
- <dt>object triples()</dt>
- <dd>Processes the <code>input</code> according to the
- <a href="#rdf-conversion-algorithm">RDF Conversion Algorithm</a>, calling
- the provided <code>tripleCallback</code> for each triple generated.
- <dl class="parameters">
- <dt>object input</dt>
- <dd>The JSON-LD object to process when outputting triples.</dd>
- <dt>JsonLdTripleCallback tripleCallback</dt>
- <dd>A callback that is called whenever a processing error occurs on
- the given <code>input</code>.
- <div class="issue">This callback should be aligned with the
- RDF API.</div></dd>
- <dt>object optional? context</dt>
- <dd>An external context to use additionally to the context embedded in <code>input</code> when expanding the <code>input</code>.</dd>
- </dl>
-
- <dl class="exception" title="InvalidContext">
- <dt>INVALID_SYNTAX</dt>
- <dd>A general syntax error was detected in the <code>@context</code>.
- For example, if a <code>@coerce</code> key maps to anything other than
- a string or an array of strings, this exception would be raised.</dd>
- <dt>MULTIPLE_DATATYPES</dt>
- <dd>There is more than one target datatype specified for a single
- property in the list of coercion rules. This means that the processor
- does not know what the developer intended for the target datatype for a
- property.</dd>
- </dl>
-
- </dd>
-
-</dl>
-
-</section>
-
-<section>
-<h3>JsonLdTripleCallback</h3>
-<p>The JsonLdTripleCallback is called whenever the processor generates a
-triple during the <code>triple()</code> call.</p>
-
-<dl title="[NoInterfaceObject Callback] interface JsonLdTripleCallback"
- class="idl">
-
- <dt>void triple()</dt>
- <dd>This callback is invoked whenever a triple is generated by the processor.
- <dl class="parameters">
- <dt>DOMString subject</dt>
- <dd>The subject IRI that is associated with the triple.</dd>
- <dt>DOMString property</dt>
- <dd>The property IRI that is associated with the triple.</dd>
- <dt>DOMString objectType</dt>
- <dd>The type of object that is associated with the triple. Valid values
- are <code>IRI</code> and <code>literal</code>.</dd>
- <dt>DOMString object</dt>
- <dd>The object value associated with the subject and the property.</dd>
- <dt>DOMString? datatype</dt>
- <dd>The datatype associated with the object.</dd>
- <dt>DOMString? language</dt>
- <dd>The language associated with the object in BCP47 format.</dd>
- </dl>
- </dd>
-</dl>
-</section>
-
-
-</section>
-
-<section>
-<h1>Algorithms</h1>
-
-<p>All algorithms described in this section are intended to operate on
-language-native data structures. That is, the serialization to a text-based
-JSON document isn't required as input or output to any of these algorithms and
-language-native data structures MUST be used where applicable.</p>
-
-<section>
- <h2>Syntax Tokens and Keywords</h2>
-
- <p>JSON-LD specifies a number of syntax tokens and keywords that are using
- in all algorithms described in this section:</p>
-
- <dl>
- <dt><code>@context</code></dt><dd>Used to set the <tref>local context</tref>.</dd>
- <dt><code>@base</code></dt><dd>Used to set the base IRI for all object IRIs affected by the <tref>active context</tref>.</dd>
- <dt><code>@vocab</code></dt><dd>Used to set the base IRI for all property IRIs affected by the <tref>active context</tref>.</dd>
- <dt><code>@coerce</code></dt><dd>Used to specify type coercion rules.</dd>
- <dt><code>@literal</code></dt><dd>Used to specify a literal value.</dd>
- <dt><code>@iri</code></dt><dd>Used to specify an IRI value.</dd>
- <dt><code>@language</code></dt><dd>Used to specify the language for a literal.</dd>
- <dt><code>@datatype</code></dt><dd>Used to specify the datatype for a literal.</dd>
- <dt><code>:</code></dt><dd>The separator for JSON keys and values that use the <tref>prefix</tref> mechanism.</dd>
- <dt><code>@subject</code></dt><dd>Sets the active subject.</dd>
- <dt><code>@type</code></dt><dd>Used to set the type of the active subject.</dd>
- </dl>
-</section>
-
-<section>
- <h2>Algorithm Terms</h2>
- <dl>
- <dt><tdef>initial context</tdef></dt>
- <dd>
- a context that is specified to the algorithm before processing begins.
- </dd>
- <dt><tdef>active subject</tdef></dt>
- <dd>
- the currently active subject that the processor should use when
- processing.
- </dd>
- <dt><tdef>active property</tdef></dt>
- <dd>
- the currently active property that the processor should use when
- processing.
- </dd>
- <dt><tdef>active object</tdef></dt>
- <dd>
- the currently active object that the processor should use when
- processing.
- </dd>
- <dt><tdef>active context</tdef></dt>
- <dd>
- a context that is used to resolve <tref>prefix</tref>es and
- <tref>term</tref>s while the processing
- algorithm is running. The <tref>active context</tref> is the context
- contained within the <tref>processor state</tref>.
- </dd>
- <dt><tdef>local context</tdef></dt>
- <dd>
- a context that is specified within a <tref>JSON object</tref>,
- specified via the <code>@context</code> keyword.
- </dd>
- <dt><tdef>processor state</tdef></dt>
- <dd>
- the <tref>processor state</tref>, which includes the <tref>active
- context</tref>, <tref>current subject</tref>, and
- <tref>current property</tref>. The <tref>processor state</tref> is managed
- as a stack with elements from the previous <tref>processor state</tref>
- copied into a new <tref>processor state</tref> when entering a new
- <tref>JSON object</tref>.
- </dd>
- <dt><tdef>JSON-LD input</tdef></dt>
- <dd>
- The JSON-LD data structure that is provided as input to the algorithm.
- </dd>
- <dt><tdef>JSON-LD output</tdef></dt>
- <dd>
- The JSON-LD data structure that is produced as output by the algorithm.
- </dd>
-
- </dl>
-</section>
-
-<section>
- <h2 id="context">Context</h2>
- <p>
- Processing of JSON-LD data structure is managed recursively.
- During processing, each rule is applied using information provided by the <tref>active context</tref>.
- Processing begins by pushing a new <tref>processor state</tref> onto the <tref>processor state</tref> stack and
- initializing the <tref>active context</tref> with the <tref>initial context</tref>. If a <tref>local context</tref> is encountered,
- information from the <tref>local context</tref> is merged into the <tref>active context</tref>.
- </p>
- <p>
- The <tref>active context</tref> is used for expanding keys and values of a <tref>JSON object</tref> (or elements
- of a list (see <span a="#list-processing">List Processing</span>)).
- </p>
- <p>
- A <tref>local context</tref> is identified within a <tref>JSON object</tref> having a key of
- <code>@context</code> with <tref>string</tref> or a <tref>JSON object</tref> value. When processing a <tref>local
- context</tref>, special processing rules apply:
- </p>
- <ol class="algorithm">
- <li>Create a new, empty <tref>local context</tref>.</li>
- <li>
- If the value is a simple <tref>string</tref>, it MUST have a lexical form of IRI and used to initialize
- a new JSON document which replaces the value for subsequent processing.
- </li>
- <li>If the value is a <tref>JSON object</tref>, perform the following steps:
- <ol class="algorithm">
- <li>
- If the <tref>JSON object</tref> has a <code>@base</code> key, it MUST have a value of a simple
- <tref>string</tref> with the lexical form of an absolute IRI. Add the base mapping to the <tref>local
- context</tref>. <p class="issue">Turtle allows @base to be relative. If we did this, we
- would have to add <a href="#iri-expansion">IRI Expansion</a>.</p>
- </li>
- <li>
- If the <tref>JSON object</tref> has a <code>@vocab</code> key, it MUST have a value of a simple
- <tref>string</tref> with the lexical form of an absolute IRI. Add the vocabulary mapping to the
- <tref>local context</tref> after performing <a href="#iri-expansion">IRI Expansion</a> on
- the associated value.
- </li>
- <li>
- If the <tref>JSON object</tref> has a <code>@coerce</code> key, it MUST have a value of a
- <tref>JSON object</tref>. Add the <code>@coerce</code> mapping to the <tref>local context</tref>
- performing <a href="#iri-expansion">IRI Expansion</a> on the associated value(s).
- </li>
- <li>
- Otherwise, the key MUST have the lexical form of <cite><a
- href="http://www.w3.org/TR/2009/REC-xml-names-20091208/#NT-NCName">NCName</a></cite> and
- MUST have the value of a simple <tref>string</tref> with the lexical form of IRI. Merge the key-value
- pair into the <tref>local context</tref>.
- </li>
- </ol>
- </li>
- <li>
- Merge the of <tref>local context</tref>'s <code>@coerce</code> mapping into the
- <tref>active context</tref>'s <code>@coerce</code> mapping as described <a href="#coerce">below</a>.
- </li>
- <li>
- Merge all entries other than the <code>@coerce</code> mapping from the <tref>local context</tref> to the
- <tref>active context</tref> overwriting any duplicate values.
- </li>
- </ol>
-
- <section>
- <h3>Coerce</h3>
- <p>
- Map each key-value pair in the <tref>local context</tref>'s
- <code>@coerce</code> mapping into the <tref>active context</tref>'s
- <code>@coerce</code> mapping, overwriting any duplicate values in
- the <tref>active context</tref>'s <code>@coerce</code> mapping.
- The <code>@coerce</code> mapping has either a single
- <code>prefix:term</code> value, a single <tref>term</tref> value or an
- <tref>array</tref> of <code>prefix:term</code> or <tref>term</tref> values.
- When merging with an existing mapping in the <tref>active context</tref>,
- map all <tref>prefix</tref> and <tref>term</tref> values to
- <tref>array</tref> form and replace with the union of the value from
- the <tref>local context</tref> and the value of the
- <tref>active context</tref>. If the result is an <tref>array</tref>
- with a single value, the processor MAY represent this as a string value.
- </p>
- </section>
-
- <section>
- <h3>Initial Context</h3>
- <p>The <tref>initial context</tref> is initialized as follows:</p>
- <ul>
- <li>
- <code>@base</code> is set using <cite><href="http://www.ietf.org/rfc/rfc2396.txt">section 5.1 Establishing a
- Base URI</href="http://www.ietf.org/rfc/rfc2396.txt"></cite> of [[RFC3986]]. Processors MAY provide a means
- of setting the base IRI programatically.
- </li>
- <li><code>@coerce</code> is set with a single mapping from <code>@iri</code> to <code>@type</code>.</li>
- </ul>
- <pre class="example" data-transform="updateExample">
- <!--
- {
- "@base": ****document-location****,
- "@coerce": {
- "@iri": "@type"
- }
- }
- -->
- </pre>
- </section>
-</section>
-
-<section>
- <h2>IRI Expansion</h2>
- <p>Keys and some values are evaluated to produce an IRI. This section defines an algorithm for
- transforming a value representing an IRI into an actual IRI.</p>
- <p>IRIs may be represented as an absolute IRI, a <tref>term</tref>, a <tref>prefix</tref>:<tref>term</tref> construct, or as a value relative to <code>@base</code>
- or <code>@vocab</code>.</p>
- <p>The algorithm for generating an IRI is:
- <ol class="algorithm">
- <li>Split the value into a <em>prefix</em> and <em>suffix</em> from the first occurrence of ':'.</li>
- <li>If the prefix is a '_' (underscore), the IRI is unchanged.</li>
- <li>If the <tref>active context</tref> contains a mapping for <em>prefix</em>, generate an IRI
- by prepending the mapped prefix to the (possibly empty) suffix using textual concatenation. Note that an empty
- suffix and no suffix (meaning the value contains no ':' string at all) are treated equivalently.</li>
- <li>If the IRI being processed is for a property (i.e., a key's value in a <tref>JSON object</tref>, or a
- value in a <code>@coerce</code> mapping) and the active context has a <code>@vocab</code> mapping,
- join the mapped value to the suffix using textual concatenation.</li>
- <li>If the IRI being processed is for a subject or object (i.e., not a property) and the active context has a <code>@base</code> mapping,
- join the mapped value to the suffix using the method described in [[!RFC3986]].</li>
- <li>Otherwise, use the value directly as an IRI.</li>
- </ol>
- </p>
-</section>
-
-<section>
- <h2>IRI Compaction</h2>
- <p>Some keys and values are expressed using IRIs. This section defines an
- algorithm for transforming an IRI to a compact IRI using the
- <tref>term</tref>s and <tref>prefix</tref>es specified in the
- <tref>local context</tref>.</p>
-
- <p>The algorithm for generating a compacted IRI is:
- <ol class="algorithm">
- <li>Search every key-value pair in the <tref>active context</tref> for
- a <tref>term</tref> that is a complete match
- against the IRI. If a complete match is found, the resulting compacted
- IRI is the <tref>term</tref> associated with the IRI in the
- <tref>active context</tref>.</li>
- <li>If a complete match is not found, search for a partial match from
- the beginning of the IRI. For all matches that are found, the resulting
- compacted IRI is the <tref>prefix</tref> associated with the partially
- matched IRI in the <tref>active context</tref> concatenated with a
- colon (:) character and the unmatched part of the string. If there is
- more than one compacted IRI produced, the final value is the
- shortest and lexicographically least value of the entire set of compacted IRIs.</li>
- </ol>
- </p>
-</section>
-
-<section>
- <h2>Value Expansion</h2>
- <p>Some values in JSON-LD can be expressed in a compact form. These values
- are required to be expanded at times when processing JSON-LD documents.
- </p>
-
- <p>The algorithm for expanding a value is:
- <ol class="algorithm">
- <li>If the key that is associated with the value has an associated
- coercion entry in the <tref>local context</tref>, the resulting
- expansion is an object populated according to the following steps:
- <ol class="algorithm">
- <li>If the coercion target is <code>@iri</code>, expand the value
- by adding a new key-value pair where the key is <code>@iri</code>
- and the value is the expanded IRI according to the
- <a href="#iri-expansion">IRI Expansion</a> rules.</li>
- <li>If the coercion target is a typed literal, expand the value
- by adding two new key-value pairs. The first key-value pair
- will be <code>@literal</code> and the unexpanded value. The second
- key-value pair will be <code>@datatype</code> and the associated
- coercion datatype expanded according to the
- <a href="#iri-expansion">IRI Expansion</a> rules.</li>
- </ol>
- </li>
- </ol>
- </p>
-</section>
-
-<section>
- <h2>Value Compaction</h2>
- <p>Some values, such as IRIs and typed literals, may be expressed in an
- expanded form in JSON-LD. These values are required to be compacted at
- times when processing JSON-LD documents.
- </p>
-
- <p>The algorithm for compacting a value is:
- <ol class="algorithm">
- <li>If the <tref>local context</tref> contains a coercion target for the
- key that is associated with the value, compact the value using the
- following steps:
- <ol class="algorithm">
- <li>If the coercion target is an <code>@iri</code>, the compacted
- value is the value associated with the <code>@iri</code> key,
- processed according to the
- <a href="#iri-compaction">IRI Compaction</a> steps.</li>
- <li>If the coercion target is a typed literal, the compacted
- value is the value associated with the <code>@literal</code> key.
- </li>
- <li>Otherwise, the value is not modified.</li>
- </ol>
- </li>
- </ol>
- </p>
-</section>
-
-<section>
-<h2>Expansion</h2>
-
-<p class="issue">This algorithm is a work in progress, do not implement it.</p>
-
-<p>As stated previously, expansion is the process of taking a JSON-LD
-input and expanding all IRIs and typed literals to their fully-expanded form.
-The output will not contain a single context declaration and will have all IRIs
-and typed literals fully expanded.
-</p>
-
-<section>
-<h3>Expansion Algorithm</h3>
-
-<ol class="algorithm">
- <li>If the top-level item in the <tref>JSON-LD input</tref> is an <tref>array</tref>,
- process each item in the <tref>array</tref> recursively using this algorithm.</li>
- <li>If the top-level item in the <tref>JSON-LD input</tref> is an object,
- update the <tref>local context</tref> according to the steps outlined in
- the <a href="#context">context</a> section. Process each key, expanding
- the key according to the <a href="#iri-expansion">IRI Expansion</a> rules.</li>
- <ol class="algorithm">
- <li>Process each value associated with each key:
- <ol class="algorithm">
- <li>If the value is an <tref>array</tref>, process each item in the <tref>array</tref>
- recursively using this algorithm.</li>
- <li>If the value is an object, process the object recursively
- using this algorithm.</li>
- <li>Otherwise, check to see the associated key has an associated
- coercion rule. If the value should be coerced, expand the value
- according to the <a href="#value-expansion">Value Expansion</a> rules.
- If the value does not need to be coerced, leave the value as-is.
- </li>
- </ol>
- <li>Remove the context from the object.</li>
- </ol>
-</ol>
-</section>
-
-</section>
-
-<section>
-<h2>Compaction</h2>
-
-<p class="issue">This algorithm is a work in progress, do not implement it.</p>
-
-<p>As stated previously, compaction is the process of taking a JSON-LD
-input and compacting all IRIs using a given context. The output
-will contain a single top-level context declaration and will only use
-<tref>term</tref>s and <tref>prefix</tref>es and will ensure that all
-typed literals are fully compacted.
-</p>
-
-<section>
-<h3>Compaction Algorithm</h3>
-
-<ol class="algorithm">
- <li>Perform the <a href="#expansion-algorithm">Expansion Algorithm</a> on
- the <tref>JSON-LD input</tref>. This removes any existing context to allow the given context to be cleanly applied.</li>
- <li>Set the <tref>active context</tref> to the given context.
- <li>If the top-level item is an <tref>array</tref>, process each item in the <tref>array</tref>
- recursively, starting at this step.
- <li>If the top-level item is an object, compress each key using the steps
- defined in <a href="#iri-compaction">IRI Compaction</a> and compress each
- value using the steps defined in
- <a href="#value-compaction">Value Compaction</a>.</li>
- </li>
-</ol>
-</section>
-
-</section>
-
-
-<section>
-<h2>Framing</h2>
-
-<p class="issue">This algorithm is a work in progress, do not implement it.</p>
-
-<p>A JSON-LD document is a representation of a directed graph. A single
-directed graph can have many different serializations, each expressing
-exactly the same information. Developers typically don't work directly with
-graphs, but rather, prefer trees when dealing with JSON. While mapping a graph
-to a tree can be done, the layout of the end result must be specified in
-advance. This section defines an algorithm for mapping a graph to
-a tree given a <tref>frame</tref>.
-</p>
-
-<section>
-<h3>Framing Algorithm Terms</h3>
- <dl>
- <dt><tdef>input frame</tdef></dt>
- <dd>
- the initial <tref>frame</tref> provided to the framing algorithm.
- </dd>
- <dt><tdef>framing context</tdef></dt>
- <dd>
- a context containing the <tref>object embed flag</tref>, the
- <tref>explicit inclusion flag</tref> and the
- <tref>omit default flag</tref>.
- </dd>
- <dt><tdef>object embed flag</tdef></dt>
- <dd>
- a flag specifying that objects should be directly embedded in the output,
- instead of being referred to by their IRI.
- </dd>
- <dt><tdef>explicit inclusion flag</tdef></dt>
- <dd>
- a flag specifying that for properties to be included in the output, they
- must be explicitly declared in the <tref>framing context</tref>.
- </dd>
- <dt><tdef>omit missing properties flag</tdef></dt>
- <dd>
- a flag specifying that properties that are missing from the
- <tref>JSON-LD input</tref> should be omitted from the output.
- </dd>
- <dt><tdef>match limit</tdef></dt>
- <dd>
- A value specifying the maximum number of matches to accept when building
- arrays of values during the framing algorithm. A value of -1 specifies
- that there is no match limit.
- </dd>
- <dt><tdef>map of embedded subjects</tdef></dt>
- <dd>
- A map that tracks if a subject has been embedded in the output of the
- <a href="#framing-algorithm">Framing Algorithm</a>.
- </dd>
- </dl>
-</section>
-
-<section>
-<h3>Framing Algorithm</h3>
-
-<p>The framing algorithm takes <tref>JSON-LD input</tref> that has been
-normalized according to the
-<a href="#normalization-algorithm">Normalization Algorithm</a>
-(<strong>normalized input</strong>), an
-<tref>input frame</tref> that has been expanded according to the
-<a href="#expansion-algorithm">Expansion Algorithm</a>
-(<strong>expanded frame</strong>), and a number of options and produces
-<tref>JSON-LD output</tref>. The following series of steps is the recursive
-portion of the framing algorithm:
-</p>
-
-<ol class="algorithm">
- <li>Initialize the <tref>framing context</tref> by setting the
- <tref>object embed flag</tref>, clearing the
- <tref>explicit inclusion flag</tref>, and clearing the
- <tref>omit missing properties flag</tref>. Override these values
- based on input options provided to the algorithm by the application.
- </li>
- <li>Generate a <tdef>list of frames</tdef> by processing the
- <strong>expanded frame</strong>:
- <ol class="algorithm">
- <li>If the <strong>expanded frame</strong> is not an <tref>array</tref>, set
- <tref>match limit</tref> to 1, place the
- <strong>expanded frame</strong> into the <tref>list of frames</tref>,
- and set the <tref>JSON-LD output</tref> to <code>null</code>.</li>
- <li>If the <strong>expanded frame</strong> is an empty <tref>array</tref>, place an
- empty object into the <tref>list of frames</tref>,
- set the <tref>JSON-LD output</tref> to an <tref>array</tref>, and set
- <tref>match limit</tref> to -1.</li>
- <li>If the <strong>expanded frame</strong> is a non-empty <tref>array</tref>, add
- each item in the <strong>expanded frame</strong> into the
- <tref>list of frames</tref>, set the <tref>JSON-LD output</tref> to an
- <tref>array</tref>, and set <tref>match limit</tref> to -1.</li>
- </ol></li>
- <li>Create a <tdef>match array</tdef> for each <strong>expanded frame</strong>
- in the <tref>list of frames</tref> halting when either the
- <tref>match limit</tref> is zero or the end of the
- <tref>list of frames</tref> is reached. If an
- <strong>expanded frame</strong> is
- not an object, the processor MUST throw a <code>Invalid Frame Format</code>
- exception. Add each matching item from the <strong>normalized input</strong>
- to the <tref>matches array</tref> and decrement the
- <tref>match limit</tref> by 1 if:
- <ol class="algorithm">
- <li>The <strong>expanded frame</strong> has an <code>rdf:type</code>
- that exists in the item's list of <code>rdf:type</code>s. Note:
- the <code>rdf:type</code> can be an <tref>array</tref>, but only one value needs
- to be in common between the item and the
- <strong>expanded frame</strong> for a match.</li>
- <li>The <strong>expanded frame</strong> does not have an
- <code>rdf:type</code> property, but every property in the
- <strong>expanded frame</strong> exists in the item.</li>
- </ol></li>
- <li>Process each item in the <tref>match array</tref> with its associated
- <tdef>match frame</tdef>:
- <ol class="algorithm">
- <li>If the <tref>match frame</tref> contains an <code>@embed</code>
- keyword, set the <tref>object embed flag</tref> to its value.
- If the <tref>match frame</tref> contains an <code>@explicit</code>
- keyword, set the <tref>explicit inclusion flag</tref> to its value.
- Note: if the keyword exists, but the value is neither
- <code>true</code> or <code>false</code>, set the associated flag to
- <code>true</code>.</li>
- <li>If the <tref>object embed flag</tref> is cleared and the item has
- the <code>@subject</code> property, replace the item with the value
- of the <code>@subject</code> property.</li>
- <li>If the <tref>object embed flag</tref> is set and the item has
- the <code>@subject</code> property, and its IRI is in the
- <tref>map of embedded subjects</tref>, throw a
- <code>Duplicate Embed</code> exception.</li>
- <li>If the <tref>object embed flag</tref> is set and the item has
- the <code>@subject</code> property and its IRI is not in the
- <tref>map of embedded subjects</tref>:
- <ol class="algorithm">
- <li>If the <tref>explicit inclusion flag</tref> is set,
- then delete any key from the item that does not exist in the
- <tref>match frame</tref>, except <code>@subject</code>.</li>
- <li>For each key in the <tref>match frame</tref>, except for
- keywords and <code>rdf:type</code>:
- <ol class="algorithm">
- <li>If the key is in the item, then build a new
- <tdef>recursion input list</tdef> using the object or objects
- associated with the key. If any object contains an
- <code>@iri</code> value that exists in the
- <tref>normalized input</tref>, replace the object in the
- <tref>recusion input list</tref> with a new object containing
- the <code>@subject</code> key where the value is the value of
- the <code>@iri</code>, and all of the other key-value pairs for
- that subject. Set the <tdef>recursion match frame</tdef> to the
- value associated with the <tref>match frame</tref>'s key. Replace
- the value associated with the key by recursively calling this
- algorithm using <tref>recursion input list</tref>,
- <tref>recursion match frame</tref> as input.</li>
- <li>If the key is not in the item, add the key to the item and
- set the associated value to an empty array if the
- <tref>match frame</tref> key's value is an array
- or <code>null</code> otherwise.</li>
- <li>If value associated with the item's key is <code>null</code>,
- process the <tref>omit missing properties flag</tref>:
- <ol class="algorithm">
- <li>If the value associated with the key in the
- <tref>match frame</tref> is an array, use the first frame
- from the array as the <tdef>property frame</tdef>, otherwise
- set the <tref>property frame</tref> to an empty object.</li>
- <li>If the <tref>property frame</tref> contains an
- <code>@omitDefault</code> keyword, set the
- <tref>omit missing properties flag</tref> to its value.
- Note: if the keyword exists, but the value is neither
- <code>true</code> or <code>false</code>, set the associated
- flag to <code>true</code>.</li>
- <li>If the <tref>omit missing properties flag</tref> is set,
- delete the key in the item. Otherwise, if the
- <code>@default</code> keyword is set in the
- <tref>property frame</tref> set the item's value to the value
- of <code>@default</code>.</li>
- </ol></li>
- </ol></li>
- </ol>
- <li>If the <tref>JSON-LD output</tref> is <code>null</code> set it to
- the item, otherwise, append the item to the
- <tref>JSON-LD output</tref>.
- </ol>
- <li>Return the <tref>JSON-LD output</tref>.</li>
-</ol>
-
-The final, non-recursive step of the framing algorithm requires the
-<tref>JSON-LD output</tref> to be compacted according to the
-<a href="#compaction-algorithm">Compaction Algorithm</a> by using the
-context provided in the <tref>input frame</tref>. The resulting value is the
-final output of the compaction algorithm and is what should be returned to the
-application.
-
-</section>
-
-</section>
-
-<section>
-<h2>Normalization</h2>
-
-<p class="issue">This algorithm is a work in progress, do not implement it.</p>
-
-<p>Normalization is the process of taking <tref>JSON-LD input</tref> and
-performing a deterministic transformation on that input that results in all
-aspects of the graph being fully expanded and named in the
-<tref>JSON-LD output</tref>. The normalized output is generated in such a way
-that any conforming JSON-LD processor will generate identical output
-given the same input. The problem is a fairly difficult technical
-problem to solve because it requires a directed graph to be ordered into a
-set of nodes and edges in a deterministic way. This is easy to do when all of
-the nodes have unique names, but very difficult to do when some of the nodes
-are not labeled.
-</p>
-
-<p>In time, there may be more than one normalization algorithm that will need
-to be identified. For identification purposes, this algorithm is named
-"Universal Graph Normalization Algorithm 2011"
-(<abbr title="Universal Graph Normalization Algorithm 2011">UGNA2011</abbr>).
-</p>
-
-<section>
-<h3>Normalization Algorithm Terms</h3>
- <dl>
- <dt><tdef>label</tdef></dt>
- <dd>
- The subject IRI associated with a graph node. The subject IRI is expressed
- using a key-value pair in a <tref>JSON object</tref> where the key is
- <code>@subject</code> and the value is a string that is an IRI or
- a <tref>JSON object</tref> containing the key <code>@iri</code> and
- a value that is a string that is an IRI.
- </dd>
- <dt><tdef>list of expanded nodes</tdef></dt>
- <dd>
- A list of all nodes in the <tref>JSON-LD input</tref> graph containing no
- embedded objects and having all keys and values expanded according to the
- steps in the <a href="#expansion-algorithm">Expansion Algorithm</a>.
- </dd>
- <dt><tdef>alpha</tdef> and <tdef>beta</tdef> values</dt>
- <dd>
- The words <tref>alpha</tref> and <tref>beta</tref> refer to the first and
- second nodes or values being examined in an algorithm. The names are
- merely used to refer to each input value to a comparison algorithm.
- </dd>
- <dt><tdef>renaming counter</tdef></dt>
- <dd>
- A counter that is used during the
- <a href="#node-relabeling-algorithm">Node Relabeling Algorithm</a>. The
- counter typically starts at one (1) and counts up for every node that is
- relabeled. There will be two such renaming counters in an implementation
- of the normalization algorithm. The first is the
- <tref>labeling counter</tref> and the second is the
- <tref>deterministic labeling counter</tref>.
- </dd>
- <dt><tdef>serialization label</tdef></dt>
- <dd>
- An identifier that is created to aid in the normalization process in the
- <a href="#deep-comparison-algorithm">Deep Comparison Algorithm</a>. The
- value typically takes the form of <code>s<NUMBER></code> or
- <code>c<NUMBER></code>.
- </dd>
-</dl>
-</section>
-
-<section>
-<h3>Normalization State</h3>
-
-<p>When performing the steps required by the normalization algorithm,
-it is helpful to track the many pieces of information in a
-data structure called the <tdef>normalization state</tdef>. Many of these
-pieces simply provide indexes into the graph. The information
-contained in the <tref>normalization state</tref> is described below.</p>
-
-<dl>
- <dt><tdef>node state</tdef></dt>
- <dd>
- Each node in the graph will be assigned a <tref>node state</tref>. This
- state contains the information necessary to deterministically
- <tref>label</tref> all nodes in the graph. A <tref>node state</tref>
- includes:
- <dl>
- <dt><tdef>node reference</tdef></dt>
- <dd>
- A <tref>node reference</tref> is a reference to a node in the graph.
- For a given <tref>node state</tref>, its <tref>node reference</tref>
- refers to the node that the state is for. When a
- <tref>node state</tref> is created, its <tref>node reference</tref>
- should be to the node it is created for.
- </dd>
- <dt><tdef>outgoing list</tdef></dt>
- <dd>
- Lists the <tref>label</tref>s for all nodes that are properties of
- the <tref>node reference</tref>. This list should be initialized
- by iterating over every object associated with a property in the
- <tref>node reference</tref> adding its label if it is another node.
- </dd>
- <dt><tdef>incoming list</tdef></dt>
- <dd>
- Lists the <tref>label</tref>s for all nodes in the graph for which
- the <tref>node reference</tref> is a property. This list is
- initialized to an empty list.
- </dd>
- <dt><tdef>outgoing serialization map</tdef></dt>
- <dd>
- Maps node <tref>label</tref>s to <tref>serialization label</tref>s.
- This map is initialized to an empty map. When this map is populated,
- it will be filled with keys that are the <tref>label</tref>s of every node in the
- graph with a label that begins with <code>_:</code> and that has a
- path, via properties, that starts with the
- <tref>node reference</tref>.
- </dd>
- <dt><tdef>outgoing serialization</tdef></dt>
- <dd>
- A string that can be lexicographically compared to the
- <tref>outgoing serialization</tref>s of other
- <tref>node state</tref>s. It is a representation of the
- <tref>outgoing serialization map</tref> and other related
- information. This string is initialized to an empty string.
- </dd>
- <dt><tdef>incoming serialization map</tdef></dt>
- <dd>
- Maps node <tref>label</tref>s to <tref>serialization label</tref>s.
- This map is initialized to an empty map. When this map is populated,
- it will be filled with keys that are the <tref>label</tref>s of every
- node in the graph with a <tref>label</tref> that begins with
- <code>_:</code> and that has a path, via properties, that ends with
- the <tref>node reference</tref>.
- </dd>
- <dt><tdef>incoming serialization</tdef></dt>
- <dd>
- A string that can be lexicographically compared to the
- <tref>outgoing serialization</tref>s of other
- <tref>node state</tref>s. It is a representation of the
- <tref>incoming serialization map</tref> and other related
- information. This string is initialized to an empty string.
- </dd>
- </dl>
- </dd>
- <dt><tdef>node state map</tdef></dt>
- <dd>
- A mapping from a node's <tref>label</tref> to a <tref>node state</tref>.
- It is initialized to an empty map.
- </dd>
- <dt><tdef>labeling prefix</tdef></dt>
- <dd>
- The labeling prefix is a string that is used as the beginning of a node
- <tref>label</tref>. It should be initialized to a random base string that
- starts with the characters <code>_:</code>, is not used by any other
- node's <tref>label</tref> in the <tref>JSON-LD input</tref>, and does not
- start with the characters <code>_:c14n</code>. The prefix has two uses.
- First it is used to temporarily name nodes during the normalization
- algorithm in a way that doesn't collide with the names that already
- exist as well as the names that will be generated by the normalization
- algorithm. Second, it will eventually be set to <code>_:c14n</code> to
- generate the final, deterministic labels for nodes in the graph. This
- prefix will be concatenated with the <tref>labeling counter</tref> to
- produce a node <tref>label</tref>. For example, <code>_:j8r3k</code> is
- a proper initial value for the <tref>labeling prefix</tref>.
- </dd>
- <dt><tdef>labeling counter</tdef></dt>
- <dd>
- A counter that is used to label nodes. It is appended to the
- <tref>labeling prefix</tref> to create a node <tref>label</tref>. It is
- initialized to <code>1</code>.
- </dd>
- <dt><tdef>map of flattened nodes</tdef></dt>
- <dd>
- A map containing a representation of all nodes in the graph where the
- key is a node <tref>label</tref> and the value is a single
- <tref>JSON object</tref> that has no nested sub-objects
- and has had all properties for the same node merged into a single
- <tref>JSON object</tref>.
- </dd>
-</dl>
-
-</section>
-
-<section>
-<h3>Normalization Algorithm</h3>
-
-<p>The normalization algorithm expands the <tref>JSON-LD input</tref>,
-flattens the data structure, and creates an initial set of names for all
-nodes in the graph. The flattened data structure is then processed by a
-node labeling algorithm in order to get a fully expanded and named list of
-nodes which is then sorted. The result is a deterministically named and
-ordered list of graph nodes.
-</p>
-
-<ol class="algorithm">
-<li>Expand the <tref>JSON-LD input</tref> according to the steps in
-the <a href="#expansion-algorithm">Expansion Algorithm</a> and store the
-result as the <strong>expanded input</strong>.</li>
-<li>Create a <tref>normalization state</tref>.</li>
-<li>Initialize the <tref>map of flattened nodes</tref> by recursively
-processing every <tdef>expanded node</tdef> in the
-<strong>expanded input</strong> in depth-first order:
- <ol class="algorithm">
- <li>If the <tref>expanded node</tref> is an unlabeled node, add a
- new key-value pair to the <tref>expanded node</tref>
- where the key is <code>@subject</code> and the value is the
- concatenation of the <tref>labeling prefix</tref>
- and the string value of the <tref>labeling counter</tref>.
- Increment the <tref>labeling counter</tref>.</li>
- <li>Add the <tref>expanded node</tref> to the
- <tref>map of flattened nodes</tref>:
- <ol class="algorithm">
- <li>If the <tref>expanded node</tref>'s <tref>label</tref> is already
- in the
- <tref>map of flattened nodes</tref> merge all properties from the
- entry in the <tref>map of flattened nodes</tref> into the
- <tref>expanded node</tref>.</li>
- <li>Go through every property associated with an array in the
- <tref>expanded node</tref> and remove any duplicate IRI entries from
- the array. If the resulting array only has one IRI entry, change it
- from an array to an object.</li>
- <li>Set the entry for the <tref>expanded node</tref>'s <tref>label</tref>
- in the <tref>map of flattened nodes</tref> to the
- <tref>expanded node</tref>.
- </li></ol></li>
- <li>After exiting the recursive step, replace the reference to the
- <tref>expanded node</tref> with an object containing a single
- key-value pair where the key is <code>@iri</code> and the value is
- the value of the <code>@subject</code> key in the node.</li>
- </ol></li>
-<li>For every entry in the <tref>map of flattened nodes</tref>, insert a
- key-value pair into the <tref>node state map</tref> where the key is the
- key from the <tref>map of flattened nodes</tref> and the value is a
- <tref>node state</tref> where its <tref>node reference</tref> refers to
- the value from the <tref>map of flattened nodes</tref>.
-<li>Populate the <tref>incoming list</tref> for each <tref>node state</tref>
- by iterating over every node in the graph and adding its <tref>label</tref>
- to the <tref>incoming list</tref> associated with each node found in its
- properties.</li>
-<li>For every entry in the <tref>node state map</tref> that has a
-<tref>label</tref> that begins with <code>_:c14n</code>, relabel the node
-using the <a href="#node-relabeling-algorithm">Node Relabeling Algorithm</a>.
-<li>Label all of the nodes that contain a <code>@subject</code> key associated
-with a value starting with <code>_:</code> according to the steps in the
-<a href="#deterministic-labeling-algorithm">Deterministic Labeling Algorithm</a>.
-</li>
-</ol>
-</section>
-
-<section>
-<h4>Node Relabeling Algorithm</h4>
-
-<p>This algorithm renames a node by generating a unique
-<tdef>new label</tdef> and updating all references to that <tref>label</tref>
-in the <tref>node state map</tref>. The <tdef>old label</tdef> and the
-<tref>normalization state</tref> must be given as an input to the
-algorithm. The <tref>old label</tref> is the current <tref>label</tref> of
-the node that is to be relabeled.
-
-<p>The node relabeling algorithm is as follows:</p>
-
-<ol class="algorithm">
- <li>If the <tref>labeling prefix</tref> is <code>_:c14n</code> and the
- <tref>old label</tref> begins with <code>_:c14n</code> then return as
- the node has already been renamed.
- </li>
- <li>Generate the <tdef>new label</tdef> by concatenating the
- <tref>labeling prefix</tref> with the string value of the
- <tref>labeling counter</tref>. Increment the <tref>labeling counter</tref>.
- </li>
- <li>For the <tref>node state</tref> associated with the
- <tref>old label</tref>, update every node in the <tref>incoming list</tref>
- by changing all the properties that reference the <tref>old label</tref> to
- the <tref>new label</tref>.
- </li>
- <li>Change the <tref>old label</tref> key in the <tref>node state map</tref>
- to the <tref>new label</tref> and set the associated
- <tref>node reference</tref>'s <tref>label</tref> to the
- <tref>new label</tref>.
- </li>
-</ol>
-</section>
-
-<section>
-<h4>Deterministic Labeling Algorithm</h4>
-
-<p>The deterministic labeling algorithm takes the
-<tref>normalization state</tref>
-and produces a <tdef>list of finished nodes</tdef> that is sorted and
-contains deterministically named and expanded nodes from the graph.
-
-<ol class="algorithm">
- <li>Set the <tref>labeling prefix</tref> to <code>_:c14n</code>, the
- <tref>labeling counter</tref> to <code>1</code>,
- the <tdef>list of finished nodes</tdef> to an empty array, and create
- an empty array, the <tdef>list of unfinished nodes</tdef>.</li>
- <li>For each <tref>node reference</tref> in the <tref>node state map</tref>:
- <ol class="algorithm">
- <li>If the node's <tref>label</tref> does not start with <code>_:</code>
- then put the <tref>node reference</tref> in the
- <tref>list of finished nodes</tref>.
- </li>
- <li>If the node's <tref>label</tref> does start with <code>_:</code>
- then put the <tref>node reference</tref> in the
- <tref>list of unfinished nodes</tref>.
- </li>
- </ol>
- </li>
- <li>Append to the <tref>list of finished nodes</tref> by processing
- the remainder of the <tref>list of unfinished nodes</tref> until it is
- empty:
- <ol class="algorithm">
- <li>Sort the <tref>list of unfinished nodes</tref> in descending order
- according to the
- <a href="#deep-comparison-algorithm">Deep Comparison Algorithm</a> to
- determine the sort order.</li>
- <li>Create a <tdef>list of labels</tdef> and initialize it to an
- empty array.</li>
- <li>For the first node from the <tref>list of unfinished nodes</tref>:
- <ol class="algorithm">
- <li>Add its <tref>label</tref> to the <tref>list of labels</tref>.
- </li>
- <li>For each key-value pair from its associated
- <tref>outgoing serialization map</tref>, add the key to a list and
- then sort the list according to the lexicographical order of the
- keys' associated values. Append the list to the
- <tref>list of nodes to label</tref>.
- </li>
- <li>For each key-value pair from its associated
- <tref>incoming serialization map</tref>, add the key to a list and
- then sort the list according to the lexicographical order of the
- keys' associated values. Append the list to the
- <tref>list of nodes to label</tref>.
- </li></ol></li>
- <li>For each <tref>label</tref> in the <tref>list of labels</tref>,
- relabel the associated node according to the
- <a href="#node-relabeling-algorithm">Node Relabeling Algorithm</a>. If
- any <tref>outgoing serialization map</tref> contains a key that
- matches the <tref>label</tref>, clear the map and set the associated
- <tref>outgoing serialization</tref> to an empty string. If any
- <tref>incoming serialization map</tref> contains a key that
- matches the <tref>label</tref>, clear the map and set the associated
- <tref>incoming serialization</tref> to an empty string.
- </li>
- <li>
- Remove each node with a <tref>label</tref> that starts with
- <code>_:c14n</code> from the <tref>list of unfinished nodes</tref> and
- add it to the <tref>list of finished nodes</tref>.
- </li>
- </ol>
- </li>
- <li>Sort the <tref>list of finished nodes</tref> in descending order
- according to the
- <a href="#deep-comparison-algorithm">Deep Comparison Algorithm</a> to
- determine the sort order.</li>
-</ol>
-</section>
-
-<section>
-<h4>Shallow Comparison Algorithm</h4>
-
-<p>
-The shallow comparison algorithm takes two unlabeled nodes,
-<tref>alpha</tref> and <tref>beta</tref>, as input and
-determines which one should come first in a sorted list. The following
-algorithm determines the steps that are executed in order to determine the
-node that should come first in a list:
-</p>
-
-<ol class="algorithm">
- <li>Compare the total number of node properties. The node with fewer
- properties is first.</li>
- <li>Lexicographically sort the property IRIs for each node and compare
- the sorted lists. If an IRI is found to be lexicographically smaller, the
- node containing that IRI is first.</li>
- <li>Compare the values of each property against one another:
- <ol class="algorithm">
- <li>The node associated with fewer property values is first.
- </li>
- <li>Create an <tdef>alpha list</tdef> by adding all values associated
- with the <tref>alpha</tref> property that are not unlabeled nodes.
- </li>
- <li>Create a <tdef>beta list</tdef> by adding all values associated
- with the <tref>beta</tref> property that is not an unlabeled node.
- </li>
- <li>Compare the length of <tref>alpha list</tref> and
- <tref>beta list</tref>. The node associated with the list containing
- the fewer number of items is first.</li>
- <li>Sort <tref>alpha list</tref> and <tref>beta list</tref> according to
- the
- <a href="#object-comparison-algorithm">Object Comparison Algorithm</a>.
- For each offset into the <tref>alpha list</tref>, compare the item
- at the offset against the item at the same offset in the
- <tref>beta list</tref> according to the
- <a href="#object-comparison-algorithm">Object Comparison Algorithm</a>.
- The node associated with the lesser item is first.
- </ol></li>
- <li>Process the <tref>incoming list</tref>s associated with each node to
- determine order:
- <ol class="algorithm">
- <li>The node with the shortest <tref>incoming list</tref> is first.</li>
- <li>Sort the <tref>incoming list</tref>s according to incoming property
- and then incoming <tref>label</tref>.
- <li>The node associated with the fewest number of incoming nodes is
- first.</li>
- <li>For each offset into the <tref>incoming list</tref>s,
- compare the associated properties and <tref>label</tref>s:
- <ol class="algorithm">
- <li>The node associated with a <tref>label</tref> that does not begin with
- <code>_:</code> is first.
- </li>
- <li>If the nodes' <tref>label</tref>s do not begin with
- <code>_:</code>, then the node associated with the
- lexicographically lesser <tref>label</tref> is first.</li>
- </li>
- <li>The node associated with the lexicographically lesser associated
- property is first.
- </li>
- <li>The node with the <tref>label</tref> that does not begin with
- <code>_:c14n</code> is first.
- </li>
- <li>The node with the lexicographically lesser <tref>label</tref>
- is first.
- </li>
- </ol>
- </ol></li>
- <li>Otherwise, the nodes are equivalent.</li>
-</section>
-
-<section>
-<h4>Object Comparison Algorithm</h4>
-
-<p>
-The object comparison algorithm is designed to compare two graph node
-property values, <tref>alpha</tref> and <tref>beta</tref>, against the other.
-The algorithm is useful when sorting two lists of graph node properties.
-</p>
-
-<ol class="algorithm">
- <li>If one of the values is a <tref>string</tref> and the other is not, the value that is
- a string is first.
- </li>
- <li>If both values are <tref>string</tref>s, the lexicographically lesser string is
- first.
- </li>
- <li>If one of the values is a literal and the other is not, the value that is
- a literal is first.
- </li>
- <li>If both values are literals:
- <ol class="algorithm">
- <li>The lexicographically lesser string associated with
- <code>@literal</code> is first.
- </li>
- <li>The lexicographically lesser string associated with
- <code>@datatype</code> is first.
- </li>
- <li>The lexicographically lesser string associated with
- <code>@language</code> is first.
- </li>
- </ol>
- </li>
- <li>If both values are expanded IRIs, the
- lexicographically lesser string associated with <code>@iri</code>
- is first.</li>
- <li>Otherwise, the two values are equivalent.</li>
-</ol>
-
-</section>
-
-<section>
-<h4>Deep Comparison Algorithm</h4>
-
-<p>
-The deep comparison algorithm is used to compare the difference between two
-nodes, <tref>alpha</tref> and <tref>beta</tref>.
-A deep comparison takes the incoming and outgoing node edges in
-a graph into account if the number of properties and value of those properties
-are identical. The algorithm is helpful when sorting a list of nodes and will
-return whichever node should be placed first in a list if the two nodes are
-not truly equivalent.
-</p>
-
-<p>When performing the steps required by the deep comparison algorithm, it
-is helpful to track state information about mappings. The information
-contained in a <tref>mapping state</tref> is described below.</p>
-
-<dl class="algorithm">
- <dt><tdef>mapping state</tdef></dt>
- <dd>
- <dl>
- <dt><tdef>mapping counter</tdef></dt>
- <dd>
- Keeps track of the number of nodes that have been mapped to
- <tref>serialization labels</tref>. It is initialized to
- <code>1</code>.
- </dd>
- <dt><tdef>processed labels map</tdef></dt>
- <dd>
- Keeps track of the <tref>label</tref>s of nodes that have already
- been assigned <tref>serialization label</tref>s. It is initialized
- to an empty map.
- </dd>
- <dt><tdef>serialized labels map</tdef></dt>
- <dd>
- Maps a node <tref>label</tref> to its associated
- <tref>serialization label</tref>. It is initialized to an empty map.
- </dd>
- <dt><tdef>adjacent info map</tdef></dt>
- <dd>
- Maps a <tref>serialization label</tref> to the node
- <tref>label</tref> associated with it, the list of sorted
- <tref>serialization label</tref>s for adjacent nodes, and the map of
- adjacent node <tref>serialiation label</tref>s to their associated
- node <tref>label</tref>s. It is initialized to an empty map.
- </dd>
- <dt><tdef>key stack</tdef></dt>
- <dd>
- A stack where each element contains an array of adjacent
- <tref>serialization label</tref>s and an index into that array. It
- is initialized to a stack containing a single element where its
- array contains a single string element <code>s1</code> and its
- index is set to <code>0</code>.
- </dd>
- <dt><tdef>serialized keys</tdef></dt>
- <dd>
- Keeps track of which <tref>serialization label</tref>s have already
- been written at least once to the <tref>serialization string</tref>.
- It is initialized to an empty map.
- </dd>
- <dt><tdef>serialization string</tdef></dt>
- <dd>
- A string that is incrementally updated as a serialization is built.
- It is initialized to an empty string.
- </dd>
- </dl>
- </dd>
-</dl>
-
-<p>The deep comparison algorithm is as follows:</p>
-
-<ol class="algorithm">
- <li>Perform a comparison between <tref>alpha</tref> and <tref>beta</tref>
- according to the
- <a href="#shallow-comparison-algorithm">Shallow Comparison Algorithm</a>.
- If the result does not show that the two nodes are equivalent, return
- the result.
- </li>
- <li>Compare incoming and outgoing edges for each node, updating their
- associated <tref>node state</tref> as each node is processed:
- <ol class="algorithm">
- <li>If the <tref>outgoing serialization map</tref> for <tref>alpha</tref>
- is empty, generate the serialization according to the
- <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
- Provide <tref>alpha</tref>'s <tref>node state</tref>, a new
- <tref>mapping state</tref>,
- <code>outgoing direction</code> to the algorithm as inputs.
- <li>If the <tref>outgoing serialization map</tref> for <tref>beta</tref>
- is empty, generate the serialization according to the
- <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
- Provide <tref>beta</tref>'s <tref>node state</tref>, a new
- <tref>mapping state</tref>, and
- <code>outgoing direction</code> to the algorithm as inputs.
- <li>If <tref>alpha</tref>'s <tref>outgoing serialization</tref> is
- lexicographically less than <tref>beta</tref>'s, then
- <tref>alpha</tref> is first. If it is greater, then <tref>beta</tref>
- is first.</li>
- <li>If the <tref>incoming serialization map</tref> for <tref>alpha</tref>
- is empty, generate the serialization according to the
- <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
- Provide <tref>alpha</tref>'s <tref>node state</tref>, a new
- <tref>mapping state</tref> with its <tref>serialized labels map</tref>
- set to a copy of <tref>alpha</tref>'s
- <tref>outgoing serialization map</tref>, and
- <code>incoming direction</code> to the algorithm as inputs.
- <li>If the <tref>incoming serialization map</tref> for <tref>beta</tref>
- is empty, generate the serialization according to the
- <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
- Provide <tref>beta</tref>'s <tref>node state</tref>, a new
- <tref>mapping state</tref> with its <tref>serialized labels map</tref>
- set to a copy of <tref>beta</tref>'s
- <tref>outgoing serialization map</tref>, and
- <code>incoming direction</code> to the algorithm as inputs.
- <li>If <tref>alpha</tref>'s <tref>incoming serialization</tref> is
- lexicographically less than <tref>beta</tref>'s, then
- <tref>alpha</tref> is first. If it is greater, then <tref>beta</tref>
- is first.</li>
- </ol></li>
-</ol>
-</section>
-
-<section>
-<h4>Node Serialization Algorithm</h4>
-
-<p>
-The node serialization algorithm takes a <tref>node state</tref>, a
-<tref>mapping state</tref>, and a <tdef>direction</tdef> (either
-<code>outgoing direction</code> or <code>incoming direction</code>) as
-inputs and generates a deterministic serialization for the
-<tref>node reference</tref>.
-</p>
-
-<ol class="algorithm">
-<li>If the <tref>label</tref> exists in the
- <tref>processed labels map</tref>, terminate the algorithm as the
- <tref>serialization label</tref> has already been created.
-</li>
-<li>Set the value associated with the <tref>label</tref> in the
- <tref>processed labels map</tref> to <code>true</code>.
-</li>
-<li>Generate the next <tdef>serialization label</tdef> for the
- <tref>label</tref> according to the
- <a href="#serialization-label-generation-algorithm">Serialization Label Generation Algorithm</a>.
-</li>
-<li>Create an empty map called the <tdef>adjacent serialized labels map</tdef>
-that will store mappings from <tref>serialized label</tref>s to adjacent
-node <tref>label</tref>s.</li>
-<li>Create an empty array called the
-<tdef>adjacent unserialized labels list</tdef> that will store
-<tref>label</tref>s of adjacent nodes that haven't been assigned
-<tref>serialization label</tref>s yet.
-</li>
-<li>For every <tref>label</tref> in a list, where the list the <tref>outgoing list</tref> if
-the <tref>direction</tref> is <code>outgoing direction</code> and the
-<tref>incoming list</tref> otherwise, if the <tref>label</tref> starts with
-<code>_:</code>, it is the <tdef>target node label</tdef>:
- <ol class="algorithm">
- <li>Look up the <tref>target node label</tref> in the
- <tref>processed labels map</tref> and if a mapping exists,
- update the <tref>adjacent serialized labels map</tref> where the key is
- the value in the <tref>serialization map</tref> and the value is the
- <tref>target node label</tref>.</li>
- <li>Otherwise, add the <tref>target node label</tref> to the
- <tref>adjacent unserialized labels list</tref>.
- </ol>
-</li>
-<li>Set the <tdef>maximum serialization combinations</tdef> to
- <code>1</code> or the length of the
- <tref>adjacent unserialized labels list</tref>, whichever is greater.</li>
-<li>While the <tref>maximum serialization combinations</tref> is greater than
- <code>0</code>, perform the
- <a href="#combinatorial-serialization-algorithm">Combinatorial Serialization Algorithm</a>
- passing the <tref>node state</tref>, the <tref>mapping state</tref> for the
- first iteration and a copy of it for each subsequent iteration, the
- generated <tref>serialization label</tref>, the <tref>direction</tref>,
- the <tref>adjacent serialized labels map</tref>, and the
- <tref>adjacent unserialized labels list</tref>.
- Decrement the <tref>maximum serialization combinations</tref> by
- <code>1</code> for each iteration.
-</ol>
-
-</section>
-
-<section>
-<h4>Serialization Label Generation Algorithm</h4>
-
-<p>
-The algorithm generates a <tref>serialization label</tref> given a
-<tref>label</tref> and a <tref>mapping state</tref> and returns the
-<tref>serialization label</tref>.
-</p>
-
- <ol class="algorithm">
- <li>If the <tref>label</tref> is already in the
- <tref>serialization labels map</tref>, return its associated value.
- </li>
- <li>If the <tref>label</tref> starts with the string <code>_:c14n</code>,
- the <tref>serialization label</tref> is the letter <code>c</code>
- followed by the number that follows <code>_:c14n</code> in the
- <tref>label</tref>.
- </li>
- <li>Otherwise, the <tref>serialization label</tref> is the
- letter <code>s</code> followed by the string value of
- <tref>mapping count</tref>. Increment the <tref>mapping count</tref> by
- <code>1</code>.
- </li>
- <li>Create a new key-value pair in the <tref>serialization labels map</tref>
- where the key is the <tref>label</tref> and the value is the
- generated <tref>serialization label</tref>.
- </li>
- </ol>
-</section>
-
-<section>
-<h4>Combinatorial Serialization Algorithm</h4>
-
-<p>
-The combinatorial serialization algorithm takes a <tref>node state</tref>, a
-<tref>mapping state</tref>, a <tref>serialization label</tref>, a
-<tref>direction</tref>, a <tref>adjacent serialized labels map</tref>,
-and a <tref>adjacent unserialized labels list</tref> as inputs and generates
-the lexicographically least serialization of nodes relating to the
-<tref>node reference</tref>.
-</p>
-
-<ol class="algorithm">
- <li>If the <tref>adjacent unserialized labels list</tref> is not empty:
- <ol class="algorithm">
- <li>Copy the <tref>adjacent serialized labels map</tref> to the
- <tdef>adjacent serialized labels map copy</tdef>.</li>
- <li>Remove the first <tref>unserialized label</tref> from the
- <tref>adjacent unserialized labels list</tref> and create a new
- <tdef>new serialization label</tdef> according to the
- <a href="#serialization-label-generation-algorithm">Serialization Label Generation Algorithm</a>.
- <li>Create a new key-value mapping in the
- <tref>adjacent serialized labels map copy</tref>
- where the key is the <tref>new serialization label</tref> and the value
- is the <tref>unserialized label</tref>.
- <li>Set the <tdef>maximum serialization rotations</tdef> to
- <code>1</code> or the length of the
- <tref>adjacent unserialized labels list</tref>, whichever is greater.
- </li>
- <li>While the <tref>maximum serialization rotations</tref> is greater than
- <code>0</code>:
- <ol class="algorithm">
- <li>Recursively perform the
- <a href="#combinatorial-serialization-algorithm">Combinatorial Serialization Algorithm</a>
- passing the <tref>mapping state</tref> for the first iteration of the
- loop, and a copy of it for each subsequent iteration.
- </li>
- <li>Rotate the elements in the
- <tref>adjacent unserialized labels list</tref> by shifting each of
- them once to the right, moving the element at the end of the list
- to the beginning of the list.
- </li>
- <li>Decrement the <tref>maximum serialization rotations</tref> by
- <code>1</code> for each iteration.
- </li>
- </ol>
- </li>
- </ol>
- </li>
- <li>If the <tref>adjacent unserialized labels list</tref> is empty:
- <ol class="algorithm">
- <li>Create a <tdef>list of keys</tdef> from the keys in the
- <tref>adjacent serialized labels map</tref> and sort it
- lexicographically.
- </li>
- <li>Add a key-value pair to the <tref>adjacent info map</tref> where
- the key is the <tref>serialization label</tref> and the value is
- an object containing the <tref>node reference</tref>'s label, the
- <tref>list of keys</tref> and the
- <tref>adjacent serialized labels map</tref>.
- </li>
- <li>Update the <tref>serialization string</tref> according to the
- <a href="#mapping-serialization-algorithm">Mapping Serialization Algorithm</a>.
- </li>
- <li>If the <tref>direction</tref> is <code>outgoing direction</code>
- then <tdef>directed serialization</tdef> refers to the
- <tref>outgoing serialization</tref> and the
- <tdef>directed serialization map</tdef> refers to the
- <tref>outgoing serialization map</tref>, otherwise it refers to the
- <tref>incoming serialization</tref> and the
- <tref>directed serialization map</tref> refers to the
- <tref>incoming serialization map</tref>. Compare the
- <tref>serialization string</tref> to the
- <tref>directed serialization</tref> according to the
- <a href="#mapping-serialization-algorithm">Serialization Comparison Algorithm</a>.
- If the <tref>serialization string</tref> is less than or equal to
- the <tref>directed serialization</tref>:
- <ol class="algorithm">
- <li>For each value in the <tref>list of keys</tref>, run the
- <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
- </li>
- <li>Update the <tref>serialization string</tref> according to the
- <a href="#mapping-serialization-algorithm">Mapping Serialization Algorithm</a>.
- </li>
- <li>Compare the <tref>serialization string</tref> to the
- <tref>directed serialization</tref> again and if it is less than
- or equal and the length of the <tref>serialization string</tref> is
- greater than or equal to the length of the
- <tref>directed serialization</tref>, then set the
- <tref>directed serialization</tref> to the
- <tref>serialization string</tref> and set the
- <tref>directed serialization map</tref> to the
- <tref>serialized labels map</tref>.
- </li>
- </ol>
- </li>
- </ol>
- </li>
-</ol>
-
-</section>
-
-<section>
-<h4>Serialization Comparison Algorithm</h4>
-
-<p>
-The serialization comparison algorithm takes two serializations,
-<tref>alpha</tref> and <tref>beta</tref> and returns either which of the two
-is less than the other or that they are equal.
-</p>
-
-<ol class="algorithm">
- <li>Whichever serialization is an empty string is greater. If they are
- both empty strings, they are equal.</li>
- <li>Return the result of a lexicographical comparison of <tref>alpha</tref>
- and <tref>beta</tref> up to the number of characters in the shortest of
- the two serializations.
- </li>
-</ol>
-</section>
-
-<section>
-<h4>Mapping Serialization Algorithm</h4>
-
-<p>
-The mapping serialization algorithm incrementally updates the
-<tref>serialization string</tref> in a <tref>mapping state</tref>.
-</p>
-
-<ol class="algorithm">
- <li>If the <tref>key stack</tref> is not empty:
- <ol class="algorithm">
- <li>Pop the <tdef>serialization key info</tdef> off of the
- <tref>key stack</tref>.
- </li>
- <li>For each <tdef>serialization key</tdef> in the
- <tref>serialization key info</tref> array, starting at
- the <tdef>serialization key index</tdef> from the
- <tref>serialization key info</tref>:
- <ol class="algorithm">
- <li>If the <tref>serialization key</tref> is not in the
- <tref>adjacent info map</tref>, push the
- <tref>serialization key info</tref> onto the
- <tref>key stack</tref> and exit from this loop.
- </li>
- <li>If the <tref>serialization key</tref> is a key in
- <tref>serialized keys</tref>, a cycle has been detected. Append
- the concatenation of the <code>_</code> character and the
- <tref>serialization key</tref> to the
- <tref>serialization string</tref>.
- <li>Otherwise, serialize all outgoing and incoming edges in the
- related node by performing the following steps:
- <ol class="algorithm">
- <li>Mark the <tref>serialization key</tref> as having
- been processed by adding a new key-value pair to
- <tref>serialized keys</tref> where the key
- is the <tref>serialization key</tref> and the value is
- <code>true</code>.
- </li>
- <li>Set the <tdef>serialization fragment</tdef> to the value of
- the <tref>serialization key</tref>.</li>
- <li>Set the <tref>adjacent info</tref> to the value of the
- <tref>serialization key</tref> in the
- <tref>adjacent info map</tref>.
- </li>
- <li>Set the <tref>adjacent node label</tref> to the node
- <tref>label</tref> from the <tref>adjacent info</tref>.
- </li>
- <li>If a mapping for the <tref>adjacent node label</tref>
- exists in the <tref>map of all labels</tref>:
- <ol class="algorithm">
- <li>Append the result of the
- <a href="">Label Serialization Algorithm</a> to the
- <tref>serialization fragment</tref>.
- </li>
- </ol>
- </li>
- <li>Append all of the keys in the <tref>adjacent info</tref>
- to the <tref>serialization fragment</tref>.
- </li>
- <li>Append the <tref>serialization fragment</tref> to the
- <tref>serialization string</tref>.
- </li>
- <li>Push a new key info object containing the keys from the
- <tref>adjacent info</tref> and an index of <code>0</code>
- onto the <tref>key stack</tref>.
- </li>
- <li>Recursively update the <tref>serialization string</tref>
- according to the
- <a href="#mapping-serialization-algorithm">Mapping Serialization Algorithm</a>.
- </li>
- </ol>
- </li>
- </ol>
- </li>
- </ol>
- </li>
-</ol>
-
-</section>
-
-<section>
-<h4>Label Serialization Algorithm</h4>
-
-<p>
-The label serialization algorithm serializes information about a node that
-has been assigned a particular <tref>serialization label</tref>.
-</p>
-
-<ol class="algorithm">
- <li>Initialize the <tref>label serialization</tref> to an empty string.</li>
- <li>Append the <code>[</code> character to the
- <tref>label serialization</tref>.</li>
- <li>Append all properties to the <tref>label serialization</tref> by
- processing each key-value pair in the <tref>node reference</tref>,
- excluding the
- <code>@subject</code> property. The keys should be processed in
- lexicographical order and their associated values should be processed
- in the order produced by the
- <a href="#object-comparison-algorithm">Object Comparison Algorithm</a>:
- <ol class="algorithm">
- <li>Build a string using the pattern <code><</code><strong>KEY</strong><code>></code>
- where <strong>KEY</strong> is the current key. Append string to the
- <tref>label serialization</tref>.</li>
- <li>The value may be a single object or an array of objects.
- Process all of the objects that are associated with the key, building
- an <tdef>object string</tdef> for each item:
- <ol class="algorithm">
- <li>If the object contains an <code>@iri</code> key with a
- value that starts
- with <code>_:</code>, set the <tref>object string</tref> to
- the value <code>_:</code>. If the value does not
- start with <code>_:</code>, build the <tref>object string</tref>
- using the pattern
- <code><</code><strong>IRI</strong><code>></code>
- where <strong>IRI</strong> is the value associated with the
- <code>@iri</code> key.</li>
- <li>If the object contains a <code>@literal</code> key and a
- <code>@datatype</code> key, build the <tref>object string</tref>
- using the pattern
- <code>"</code><strong>LITERAL</strong><code>"^^<</code><strong>DATATYPE</strong><code>></code>
- where <strong>LITERAL</strong> is the value associated with the
- <code>@literal</code> key and <strong>DATATYPE</strong> is the
- value associated with the <code>@datatype</code> key.</li>
- <li>If the object contains a <code>@literal</code> key and a
- <code>@language</code> key, build the <tref>object string</tref>
- using the pattern
- <code>"</code><strong>LITERAL</strong><code>"@</code><strong>LANGUAGE</strong>
- where <strong>LITERAL</strong> is the value associated with the
- <code>@literal</code> key and <strong>LANGUAGE</strong> is the
- value associated with the <code>@language</code> key.</li>
- <li>Otherwise, the value is a string. Build the
- <tref>object string</tref> using the pattern
- <code>"</code><strong>LITERAL</strong><code>"</code>
- where <strong>LITERAL</strong> is the value associated with the
- current key.</li>
- <li>If this is the second iteration of the loop,
- append a <code>|</code> separator character to the
- <tref>label serialization</tref>.</li>
- <li>Append the <tref>object string</tref> to the
- <tref>label serialization</tref>.</li>
- </ol>
- </ol>
- </li>
- <li>Append the <code>]</code> character to the
- <tref>label serialization</tref>.</li>
- <li>Append the <code>[</code> character to the
- <tref>label serialization</tref>.</li>
- <li>Append all incoming references for the current
- <tref>label</tref> to the <tref>label serialization</tref> by
- processing all of the items associated with the <tref>incoming list</tref>:
- <ol class="algorithm">
- <li>Build a <tdef>reference string</tdef>
- using the pattern <code><</code><strong>PROPERTY</strong><code>></code><code><</code><strong>REFERER</strong><code>></code>
- where <strong>PROPERTY</strong> is the property associated with the
- incoming reference and <strong>REFERER</strong> is either the subject of
- the node referring to the <tref>label</tref> in the incoming reference
- or <code>_:</code> if <strong>REFERER</strong> begins with
- <code>_:</code>.
- <li>If this is the second iteration of the loop,
- append a <code>|</code> separator character to the
- <tref>label serialization</tref>.</li>
- <li>Append the <tref>reference string</tref> to the
- <tref>label serialization</tref>.</li>
- </ol>
- <li>Append the <code>]</code> character to the
- <tref>label serialization</tref>.</li>
- <li>Append all <tref>adjacent node labels</tref> to the
- <tref>label serialization</tref> by concatenating the string value
- for all of them, one after the other, to the
- <tref>label serialization</tref>.</li>
- <li>Push the <tref>adjacent node labels</tref> onto the
- <tref>key stack</tref> and append the result of the
- <a href="#mapping-serialization-algorithm">Mapping Serialization Algorithm</a>
- to the <tref>label serialization</tref>.
-</ol>
-
-</section>
-
-</section>
-
-<section>
-
-<h3>Data Round Tripping</h3>
-
-<p>When normalizing <strong>xsd:double</strong> values, implementers MUST
-ensure that the normalized value is a string. In order to generate the
-string from a <strong>double</strong> value, output equivalent to the
-<code>printf("%1.6e", value)</code> function in C MUST be used where
-<strong>"%1.6e"</strong> is the string formatter and <strong>value</strong>
-is the value to be converted.</p>
-
-<p>To convert the a double value in JavaScript, implementers can use the
-following snippet of code:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-// the variable 'value' below is the JavaScript native double value that is to be converted
-(value).toExponential(6).replace(/(e(?:\+|-))([0-9])$/, '$10$2')
--->
-</pre>
-
-<p class="note">When data needs to be normalized, JSON-LD authors should
-not use values that are going to undergo automatic conversion. This is due
-to the lossy nature of <strong>xsd:double</strong> values.</p>
-
-<p class="note">Some JSON serializers, such as PHP's native implementation,
-backslash-escapes the forward slash character. For example, the value
-<code>http://example.com/</code> would be serialized as
-<code>http:\/\/example.com\/</code> in some
-versions of PHP. This is problematic when generating a byte
-stream for processes such as normalization. There is no need to
-backslash-escape forward-slashes in JSON-LD. To aid interoperability between
-JSON-LD processors, a JSON-LD serializer MUST NOT backslash-escape
-forward slashes.</p>
-
-<p class="issue">Round-tripping data can be problematic if we mix and
-match @coerce rules with JSON-native datatypes, like integers. Consider the
-following code example:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-var myObj = { "@context" : {
- "number" : "http://example.com/vocab#number",
- "@coerce": {
- "xsd:nonNegativeInteger": "number"
- }
- },
- "number" : 42 };
-
-// Map the language-native object to JSON-LD
-var jsonldText = jsonld.normalize(myObj);
-
-// Convert the normalized object back to a JavaScript object
-var myObj2 = jsonld.parse(jsonldText);
--->
-</pre>
-
-<p class="issue">At this point, myObj2 and myObj will have different
-values for the "number" value. myObj will be the number 42, while
-myObj2 will be the string "42". This type of data round-tripping
-error can bite developers. We are currently wondering if having a
-"coerce validation" phase in the parsing/normalization phases would be a
-good idea. It would prevent data round-tripping issues like the
-one mentioned above.</p>
-
-</section>
-
-<section>
-<h2>RDF Conversion</h2>
-
-<p>A JSON-LD document MAY be converted to any other RDF-compatible document
-format using the algorithm specified in this section.</p>
-
-<p>
- The JSON-LD Processing Model describes processing rules for extracting RDF
- from a JSON-LD document. Note that many uses of JSON-LD may not require
- generation of RDF.
-</p>
-
-<p>
-The processing algorithm described in this section is provided in
-order to demonstrate how one might implement a JSON-LD to RDF processor.
-Conformant implementations are only required to produce the same type and
-number of triples during the output process and are not required to
-implement the algorithm exactly as described.
-</p>
-
-<p class="issue">The RDF Conversion Algorithm is a work in progress.</p>
-
-<section class="informative">
- <h4>Overview</h4>
- <p>
- JSON-LD is intended to have an easy to parse grammar that closely models existing
- practice in using JSON for describing object representations. This allows the use
- of existing libraries for parsing JSON.
- </p>
- <p>
- As with other grammars used for describing <tref>Linked Data</tref>, a key concept is that of
- a <em>resource</em>. Resources may be of three basic types: <em>IRI</em>s, for describing
- externally named entities, <em>BNodes</em>, resources for which an external name does not
- exist, or is not known, and Literals, which describe terminal entities such as strings,
- dates and other representations having a lexical representation possibly including
- an explicit language or datatype.
- </p>
- <p>
- Data described with JSON-LD may be considered to be the representation of a graph made
- up of <tref>subject</tref> and <tref>object</tref> resources related via a <tref>property</tref> resource.
- However, specific implementations may choose to operate on the document as a normal
- JSON description of objects having attributes.
- </p>
-</section>
-
-<section>
- <h4>RDF Conversion Algorithm Terms</h4>
- <dl>
- <dt><tdef>default graph</tdef></dt>
- <dd>
- the destination graph for all triples generated by JSON-LD markup.
- </dd>
- </dl>
-</section>
-
-<section>
- <h3>RDF Conversion Algorithm</h3>
- <p>
- The algorithm below is designed for in-memory implementations with random access to <tref>JSON object</tref> elements.
- </p>
- <p>
- A conforming JSON-LD processor implementing RDF conversion MUST implement a
- processing algorithm that results in the same <tref>default graph</tref> that the following
- algorithm generates:
- </p>
-
- <ol class="algorithm">
- <li id="processing-step-default-context">
- Create a new <tref>processor state</tref> with with the <tref>active context</tref> set to the
- <tref>initial context</tref> and <tref>active subject</tref> and <tref>active property</tref>
- initialized to NULL.
- </li>
-
- <li id="processing-step-associative">
- If a <tref>JSON object</tref> is detected, perform the following steps:
- <ol class="algorithm">
- <li>
- If the <tref>JSON object</tref> has a <code>@context</code> key, process the local context as
- described in <a href="#context">Context</a>.
- </li>
- <li>
- Create a new <tref>JSON object</tref> by mapping the keys from the current <tref>JSON object</tref> using the
- <tref>active context</tref> to new keys using the associated value from the current <tref>JSON object</tref>.
- Repeat the mapping until no entry is found within the <tref>active context</tref> for the key. Use the new
- <tref>JSON object</tref> in subsequent steps.
- </li>
- <li>
- If the <tref>JSON object</tref> has an <code>@iri</code> key, set the <tref>active object</tref> by
- performing <a href="#iri-expansion">IRI Expansion</a> on the associated value. Generate a
- triple representing the <tref>active subject</tref>, the <tref>active property</tref> and the
- <tref>active object</tref>. Return the <tref>active object</tref> to the calling location.
- <p class="issue"><code>@iri</code> really just behaves the same as <code>@subject</code>, consider consolidating them.</p>
- </li>
- <li>
- If the <tref>JSON object</tref> has a <code>@literal</code> key, set the <tref>active object</tref>
- to a literal value as follows:
- <ol class="algorithm">
- <li>
- as a <tref>typed literal</tref> if the <tref>JSON object</tref> contains a <code>@datatype</code> key
- after performing <a href="#iri-expansion">IRI Expansion</a> on the specified<code>@datatype</code>.
- </li>
- <li>
- otherwise, as a <tref>plain literal</tref>. If the <tref>JSON object</tref> contains
- a <code>@language</code> key, use it's value to set the language of the plain literal.
- </li>
- <li>
- Generate a triple representing the <tref>active subject</tref>, the <tref>active property</tref> and the
- <tref>active object</tref>. Return the <tref>active object</tref> to the calling location.
- </li>
- </ol>
- </li>
- <li id="processing-step-subject">If the <tref>JSON object</tref> has a <code>@subject</code> key:
- <ol class="algorithm">
- <li>
- If the value is a <tref>string</tref>, set the <tref>active object</tref> to the result of performing
- <a href="#iri-expansion">IRI Expansion</a>. Generate a
- triple representing the <tref>active subject</tref>, the <tref>active property</tref> and the
- <tref>active object</tref>. Set the <tref>active subject</tref> to the <tref>active object</tref>.
- </li>
- <li>
- Create a new <tref>processor state</tref> using copies of the <tref>active context</tref>,
- <tref>active subject</tref> and <tref>active property</tref> and process the value
- starting at <a href="#processing-step-associative">Step 2</a>, set the <tref>active
- subject</tref> to the result and proceed using the previous <tref>processor state</tref>.
- </li>
- </ol>
- </li>
- <li>
- If the <tref>JSON object</tref> does not have a <code>@subject</code> key, set the <tref>active
- object</tref> to newly generated <tdef>blank node identifier</tdef>. Generate a triple
- representing the <tref>active subject</tref>, the <tref>active property</tref> and the
- <tref>active object</tref>. Set the <tref>active subject</tref> to the <tref>active
- object</tref>.
- </li>
- <li>
- For each key in the <tref>JSON object</tref> that has not already been processed, perform
- the following steps:
- <ol class="algorithm">
- <li>
- If the key is <code>@type</code>, set the <tref>active property</tref>
- to <code>rdf:type</code>.
- </li>
- <li>Otherwise, set the <tref>active property</tref> to the result of performing
- <a href="#iri-expansion">IRI Expansion</a> on the key.</li>
- <li>
- Create a new <tref>processor state</tref> copies of the <tref>active context</tref>,
- <tref>active subject</tref> and <tref>active property</tref> and process the value
- starting at <a href="#processing-step-associative">Step 2</a> and proceed using the
- previous <tref>processor state</tref>.
- </li>
- </ol>
- </li>
- <li>
- Return the <tref>active object</tref> to the calling location.
- </li>
- </ol>
- </li>
-
- <li>
- If a regular <tref>array</tref> is detected, process each value in the <tref>array</tref> by doing the following
- returning the result of processing the last value in the <tref>array</tref>:
-
- <ol class="algorithm">
- <li>
- Create a new <tref>processor state</tref> using copies of the <tref>active
- context</tref>, <tref>active subject</tref> and <tref>active property</tref> and process the value
- starting at <a href="#processing-step-associative">Step 2</a> then proceed using the previous
- <tref>processor state</tref>.
- </li>
- </ol>
- </li>
-
- <li>
- If a <tref>string</tref> is detected:
- <ol class="algorithm">
- <li>
- If the <tref>active property</tref> is the target of a <code>@iri</code> coercion,
- set the <tref>active object</tref> by
- performing <a href="#iri-expansion">IRI Expansion</a> on the string.
- </li>
- <li>
- Otherwise, if the <tref>active property</tref> is the target of coercion,
- set the <tref>active object</tref> by creating a <tref>typed literal</tref> using
- the string and the coercion key as the datatype IRI.
- </li>
- <li>
- Otherwise, set the <tref>active object</tref> to a <tref>plain literal</tref> value created from
- the string.
- </li>
- </ol>
- Generate a
- triple representing the <tref>active subject</tref>, the <tref>active property</tref> and the
- <tref>active object</tref>.
- </li>
-
- <li>
- If a <tref>number</tref> is detected, generate a <tref>typed literal</tref> using a string representation of
- the value with datatype set to either <code>xsd:integer</code> or
- <code>xsd:double</code>, depending on if the value contains a
- fractional and/or an exponential component. Generate a triple using the <tref>active
- subject</tref>, <tref>active property</tref> and the generated typed literal.
- </li>
-
- <li>
- Otherwise, if <strong>true</strong> or <strong>false</strong> is detected,
- generate a triple using the <tref>active subject</tref>, <tref>active property</tref>
- and a <tref>typed literal</tref> value created from the string representation of the
- value with datatype set to <code>xsd:boolean</code>.
- </li>
- </ol>
-</section>
-
-<!-- THIS SHOULD BE SPLIT OUT INTO A SEPARATE DOCUMENT
-
-<section>
-<h1>Best Practices</h1>
-
-<p>The nature of Web programming allows one to use basic technologies, such as
-JSON-LD, across a variety of systems and environments. This section attempts to
-describe some of those environments and the way in which JSON-LD can be
-integrated in order to help alleviate certain development headaches.
-</p>
-
-<section>
-<h2>JavaScript</h2>
-
-<p class="issue">It is expected that JSON-LD will be used quite a bit in
-JavaScript environments, however, features like the expanded form for
-object values mean that using JSON-LD directly in JavaScript may be
-annoying without a middleware layer such as a simple library that
-converts JSON-LD markup before JavaScript uses it. One could say that JSON-LD
-is a good fit for the RDF API, which enables a variety of RDF-based
-Web Applications, but some don't want to require that level of functionality
-just to use JSON-LD. The group is still discussing the best way to proceed,
-so input on how JSON-LD could more easily be utilized in JavaScript
-environments would be very much appreciated.
-</p>
-</section>
-
-<section>
-<h2>Schema-less Databases</h2>
-
-<p class="issue">Databases such as CouchDB and MongoDB allow the creation of
-schema-less data stores. RDF is a type of schema-less data model and thus
-lends itself to databases such as CouchDB and MongoDB. Both of these databases
-can use JSON-LD as their storage format. The group needs feedback from
-CouchDB and MongoDB experts regarding the usefulness of JSON-LD in those
-environments.</p>
-
-<p class="issue">MongoDB does not allow the '.' character to be used in
-key names. This prevents developers from storing IRIs as keys, which also
-prevents storage of the data in normalized form. While this issue can
-be avoided by using <tref>prefix</tref>es for key values, it is not known if this
-mechanism is enough to allow JSON-LD to be used in MongoDB in a way that
-is useful to developers.
-</p>
-
--->
-</section>
-
-</section>
-
-<section class="appendix">
-<h1>Experimental Concepts</h1>
-
-<p class="issue">There are a few advanced concepts where it is not clear
-whether or not the JSON-LD specification is going to support the complexity
-necessary to support each concept. The entire section on Advanced Concepts
-should be considered as discussion points; it is merely a list of
-possibilities where all of the benefits and drawbacks have not been explored.
-</p>
-
-<section>
-<h2>Disjoint Graphs</h2>
-
-<p>When serializing an RDF graph that contains two or more sections of the
-graph which are entirely disjoint, one must use an <tref>array</tref> to express the graph
-as two graphs. This may not be acceptable to some authors, who would rather
-express the information as one graph. Since, by definition, disjoint graphs
-require there to be two top-level objects, JSON-LD utilizes a mechanism that
-allows disjoint graphs to be expressed using a single graph.</p>
-
-<p>Assume the following RDF graph:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-<http://example.org/people#john>
- <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
- <http://xmlns.com/foaf/0.1/Person> .
-<http://example.org/people#jane>
- <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
- <http://xmlns.com/foaf/0.1/Person> .
--->
-</pre>
-
-<p>Since the two subjects are entirely disjoint with one another, it is
-impossible to express the RDF graph above using a single <tref>JSON object</tref>.</p>
-
-<p>In JSON-LD, one can use the subject to express disjoint graphs as a
-single graph:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "@context": {
- "Person": "http://xmlns.com/foaf/0.1/Person"
- },
- "@subject":
- [
- {
- "@subject": "http://example.org/people#john",
- "@type": "Person"
- },
- {
- "@subject": "http://example.org/people#jane",
- "@type": "Person"
- }
- ]
-}
--->
-</pre>
-
-<p>A disjoint graph could also be expressed like so:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-[
- {
- "@subject": "http://example.org/people#john",
- "@type": "http://xmlns.com/foaf/0.1/Person"
- },
- {
- "@subject": "http://example.org/people#jane",
- "@type": "http://xmlns.com/foaf/0.1/Person"
- }
-]
--->
-</pre>
-
-<p class="note">Warning: Using this serialisation format it is impossible to include <code>@context</code>
- given that the document's data structure is an array and not an object.</p>
-
-</section>
-
-<section>
- <h2>Lists</h2>
- <p>
- Because graphs do not describe ordering for links between nodes, in contrast to plain JSON, multi-valued properties
- in JSON-LD do not provide an ordering of the listed objects. For example, consider the following
- simple document:
- </p>
- <pre class="example" data-transform="updateExample">
- <!--
- {
- ...
- "@subject": "http://example.org/people#joebob",
- "nick": ****["joe", "bob", "jaybee"]****,
- ...
- }
- -->
- </pre>
- <p>
- This results in three triples being generated, each relating the subject to an individual
- object, with no inherent order.</p>
- <p>To preserve the order of the objects, RDF-based languages, such as [[TURTLE]]
- use the concept of an <code>rdf:List</code> (as described in [[RDF-SCHEMA]]). This uses a sequence
- of unlabeled nodes with properties describing a value, a null-terminated next property. Without
- specific syntactical support, this could be represented in JSON-LD as follows:
- </p>
- <pre class="example" data-transform="updateExample">
- <!--
- {
- ...
- "@subject": "http://example.org/people#joebob",
- "nick": ****{****,
- ****"@first": "joe"****,
- ****"@rest": {****
- ****"@first": "bob"****,
- ****"@rest": {****
- ****"@first": "jaybee"****,
- ****"@rest": "@nil"****
- ****}****
- ****}****
- ****}****
- ****}****,
- ...
- }
- -->
- </pre>
- <p>
- As this notation is rather unwieldy and the notion of ordered collections is rather important
- in data modeling, it is useful to have specific language support. In JSON-LD, a list may
- be represented using the <code>@list</code> keyword as follows:
- </p>
- <pre class="example" data-transform="updateExample">
- <!--
- {
- ...
- "@subject": "http://example.org/people#joebob",
- "foaf:nick": ****{"@list": ["joe", "bob", "jaybee"]}****,
- ...
- }
- -->
- </pre>
- <p>
- This describes the use of this <tref>array</tref> as being ordered, and order is maintained through
- normalization and RDF conversion. If every use of a given multi-valued property is a
- list, this may be abbreviated by adding an <code>@coerce</code> term:
- </p>
- <pre class="example" data-transform="updateExample">
- <!--
- {
- ****"@context": {****
- ...
- ****"@coerce": {****
- ****"@list": ["foaf:nick"]****
- ****}****
- ****}****,
- ...
- "@subject": "http://example.org/people#joebob",
- "foaf:nick": ****["joe", "bob", "jaybee"]****,
- ...
- }
- -->
- </pre>
- <p class="issue">There is an ongoing discussion about this issue. One of the <a href="https://github.com/json-ld/json-ld.org/issues/12">proposed solutions</a> is allowing to change the default behaviour so that arrays are considered as ordered lists by default.</p>
- <section><h3 id="list-expansion">Expansion</h3>
- <p class="issue">TBD.</p>
- </section>
- <section><h3 id="list-normalization">Normalization</h3>
- <p class="issue">TBD.</p>
- </section>
- <section><h3 id="list-rdf">RDF Conversion</h3>
- <p>
- To support RDF Conversion of lists, <a href="#rdf-conversion-algorithm">RDF Conversion Algorithm</a>
- is updated as follows:
- </p>
- <ol class="algorithm update">
- <li>
- <span class="list-number">2.4a.</span>
- If the <tref>JSON object</tref> has a <code>@list</code> key and the value is an <tref>array</tref>
- process the value as a list starting at <a href="#processing-step-list">Step 3a</a>.
- </li>
- <li>
- <span class="list-number">2.7.3.</span>
- Create a new <tref>processor state</tref> copies of the <tref>active context</tref>,
- <tref>active subject</tref> and <tref>active property</tref>.
- <ol class="algorithm">
- <li>
- If the <tref>active property</tref> is the target of a <code>@list</code> coercion,
- and the value is an <tref>array</tref>,
- process the value as a list starting at <a href="#processing-step-list">Step 3a</a>.
- </li>
- <li>
- Otherwise, process the value starting at
- <a href="#processing-step-associative">Step 2</a>.
- </li>
- <li>Proceed using the previous <tref>processor state</tref>.</li>
- </ol>
- </li>
- <li id="processing-step-list">
- <span class="list-number">3a.</span>
- Generate an RDF List by linking
- each element of the list using <code>rdf:first</code> and <code>rdf:next</code>, terminating the list with <code>rdf:nil</code>
- using the following sequence:
- <ol class="algorithm">
- <li>
- If the list has no element, generate a triple using the <tref>active subject</tref>, <tref>active property</tref>
- and <code>rdf:nil</code>.
- </li>
- <li>
- Otherwise, generate a triple using using the <tref>active subject</tref>, <tref>active property</tref>
- and a newly generated BNode identified as <em>first <tdef>blank node identifier</tdef></em>.
- </li>
- <li>
- For each element other than the last element in the list:
- <ol class="algorithm">
- <li>Create a processor state using the active context, <em>first <tdef>blank node identifier</tdef></em> as the <tref>active subject</tref>, and <code>rdf:first</code> as the <tref>active property</tref>.</li>
- <li>Unless this is the last element in the list, generate a new BNode identified as <em>rest <tdef>blank node identifier</tdef></em>, otherwise use <code>rdf:nil</code>.</li>
- <li>Generate a new triple using <em>first <tdef>blank node identifier</tdef></em>, <code>rdf:rest</code> and <em>rest <tdef>blank node identifier</tdef></em>.</li>
- <li>Set <em>first <tdef>blank node identifier</tdef></em> to <em>rest <tdef>blank node identifier</tdef></em>.</li>
- </ol>
- </li>
- </ol>
- </li>
- </ol>
- </section>
-</section>
-
-</section>
-
-<section class="appendix">
-<h2>Markup Examples</h2>
-
-<p>The JSON-LD markup examples below demonstrate how JSON-LD can be used to
-express semantic data marked up in other languages such as RDFa, Microformats,
-and Microdata. These sections are merely provided as proof that JSON-LD is
-very flexible in what it can express across different Linked Data approaches.
-</p>
-
-<section>
-<h3>RDFa</h3>
-
-<p>The following example describes three people with their respective names and
-homepages.</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-<div ****prefix="foaf: http://xmlns.com/foaf/0.1/"****>
- <ul>
- <li ****typeof="foaf:Person"****>
- <a ****rel="foaf:homepage" href="http://example.com/bob/" property="foaf:name" ****>Bob</a>
- </li>
- <li ****typeof="foaf:Person"****>
- <a ****rel="foaf:homepage" href="http://example.com/eve/" property="foaf:name" ****>Eve</a>
- </li>
- <li ****typeof="foaf:Person"****>
- <a ****rel="foaf:homepage" href="http://example.com/manu/" property="foaf:name" ****>Manu</a>
- </li>
- </ul>
-</div>
--->
-</pre>
-
-<p>An example JSON-LD implementation is described below, however, there are
-other ways to mark-up this information such that the context is not
-repeated.</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "@context": { "foaf": "http://xmlns.com/foaf/0.1/"},
- "@subject": [
- {
- "@subject": "_:bnode1",
- "@type": "foaf:Person",
- "foaf:homepage": "http://example.com/bob/",
- "foaf:name": "Bob"
- },
- {
- "@subject": "_:bnode2",
- "@type": "foaf:Person",
- "foaf:homepage": "http://example.com/eve/",
- "foaf:name": "Eve"
- },
- {
- "@subject": "_:bnode3",
- "@type": "foaf:Person",
- "foaf:homepage": "http://example.com/manu/",
- "foaf:name": "Manu"
- }
- ]
-}
--->
-</pre>
-
-</section>
-
-<section>
-<h3>Microformats</h3>
-
-<p>The following example uses a simple Microformats hCard example to express
-how the Microformat is represented in JSON-LD.</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-<div class="vcard">
- <a class="url fn" href="http://tantek.com/">Tantek Çelik</a>
-</div>
--->
-</pre>
-
-<p>The representation of the hCard expresses the Microformat terms in the
-context and uses them directly for the <code>url</code> and <code>fn</code>
-properties. Also note that the Microformat to JSON-LD processor has
-generated the proper URL type for <code>http://tantek.com</code>.</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "@context":
- {
- "vcard": "http://microformats.org/profile/hcard#vcard",
- "url": "http://microformats.org/profile/hcard#url",
- "fn": "http://microformats.org/profile/hcard#fn",
- "@coerce": { "@iri": "url" }
- },
- "@subject": "_:bnode1",
- "@type": "vcard",
- "url": "http://tantek.com/",
- "fn": "Tantek Çelik"
-}
--->
-</pre>
-
-</section>
-
-<section>
-<h3>Microdata</h3>
-
-<p>The Microdata example below expresses book information as a Microdata Work
-item.
-</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-<dl itemscope
- itemtype="http://purl.org/vocab/frbr/core#Work"
- itemid="http://purl.oreilly.com/works/45U8QJGZSQKDH8N">
- <dt>Title</dt>
- <dd><cite itemprop="http://purl.org/dc/terms/title">Just a Geek</cite></dd>
- <dt>By</dt>
- <dd><span itemprop="http://purl.org/dc/terms/creator">Wil Wheaton</span></dd>
- <dt>Format</dt>
- <dd itemprop="http://purl.org/vocab/frbr/core#realization"
- itemscope
- itemtype="http://purl.org/vocab/frbr/core#Expression"
- itemid="http://purl.oreilly.com/products/9780596007683.BOOK">
- <link itemprop="http://purl.org/dc/terms/type" href="http://purl.oreilly.com/product-types/BOOK">
- Print
- </dd>
- <dd itemprop="http://purl.org/vocab/frbr/core#realization"
- itemscope
- itemtype="http://purl.org/vocab/frbr/core#Expression"
- itemid="http://purl.oreilly.com/products/9780596802189.EBOOK">
- <link itemprop="http://purl.org/dc/terms/type" href="http://purl.oreilly.com/product-types/EBOOK">
- Ebook
- </dd>
-</dl>
--->
-</pre>
-
-<p>Note that the JSON-LD representation of the Microdata information stays
-true to the desires of the Microdata community to avoid contexts and
-instead refer to items by their full IRI.</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-[
- {
- "@subject": "http://purl.oreilly.com/works/45U8QJGZSQKDH8N",
- "@type": "http://purl.org/vocab/frbr/core#Work",
- "http://purl.org/dc/terms/title": "Just a Geek",
- "http://purl.org/dc/terms/creator": "Whil Wheaton",
- "http://purl.org/vocab/frbr/core#realization":
- ["http://purl.oreilly.com/products/9780596007683.BOOK", "http://purl.oreilly.com/products/9780596802189.EBOOK"]
- },
- {
- "@subject": "http://purl.oreilly.com/products/9780596007683.BOOK",
- "@type": "http://purl.org/vocab/frbr/core#Expression",
- "http://purl.org/dc/terms/type": "http://purl.oreilly.com/product-types/BOOK"
- },
- {
- "@subject": "http://purl.oreilly.com/products/9780596802189.EBOOK",
- "@type": "http://purl.org/vocab/frbr/core#Expression",
- "http://purl.org/dc/terms/type": "http://purl.oreilly.com/product-types/EBOOK"
- }
-]
--->
-</pre>
-</section>
-</section>
-
-<section class="appendix">
-<h3>Mashing Up Vocabularies</h3>
-
-<p>Developers would also benefit by allowing other vocabularies to be used
-automatically with their JSON API. There are over 200
-<tref>Web Vocabulary</tref> Documents that are available for use on the Web
-today. Some of these vocabularies are:
-</p>
-
-<ul>
- <li>RDF - for describing information about objects and concepts on the Web.</li>
- <li>RDFS - for expressing things like labels and comments.</li>
- <li>XSD - for specifying basic types like strings, integers, dates and times.</li>
- <li>Dublin Core - for describing creative works.</li>
- <li>FOAF - for describing social networks.</li>
- <li>Calendar - for specifying events.</li>
- <li>SIOC - for describing discussions on blogs and websites.</li>
- <li>CCrel - for describing Creative Commons and other types of licenses.</li>
- <li>GEO - for describing geographic location.</li>
- <li>VCard - for describing organizations and people.</li>
- <li>DOAP - for describing projects.</li>
-</ul>
-
-<p>You can use these vocabularies in combination, like so:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- "****@type****": "****foaf:Person****",
- "****foaf:name****": "Manu Sporny",
- "****foaf:homepage****": "http://manu.sporny.org/",
- "****sioc:avatar****": "http://twitter.com/account/profile_image/manusporny"
-}
--->
-</pre>
-
-<p>Developers can also specify their own Vocabulary documents by modifying the
-<tref>active context</tref> in-line using the <code>@context</code> keyword,
-like so:</p>
-
-<pre class="example" data-transform="updateExample">
-<!--
-{
- ****"@context": { "myvocab": "http://example.org/myvocab#" }****,
- "@type": "foaf:Person",
- "foaf:name": "Manu Sporny",
- "foaf:homepage": "http://manu.sporny.org/",
- "sioc:avatar": "http://twitter.com/account/profile_image/manusporny"****,
- "myvocab:personality": "friendly"****
-}
-
--->
-</pre>
-
-<p>The <code>@context</code> keyword is used to change how the JSON-LD
-processor evaluates key-value pairs. In this case, it was used to
-map one string ('myvocab') to another string, which is interpreted as
-a <tref>IRI</tref>. In the example above, the <code>myvocab</code> string is replaced
-with "<code>http://example.org/myvocab#</code>" when it
-is detected. In the example above, "<code>myvocab:personality</code>" would
-expand to "<code>http://example.org/myvocab#personality</code>".</p>
-
-<p>This mechanism is a short-hand, called a <tref>Web Vocabulary</tref> <tref>prefix</tref>,
-and provides developers an unambiguous way to map any JSON value to RDF.<p>
-
-</section>
-
-<section class="appendix">
-<h1>IANA Considerations</h1>
-
-<p>This section is included merely for standards community review and will be
-submitted to the Internet Engineering Steering Group if this specification
-becomes a W3C Recommendation.</p>
-
-<dl>
- <dt>Type name:</dt>
- <dd>application</dd>
- <dt>Subtype name:</dt>
- <dd>ld+json</dd>
- <dt>Required parameters:</dt>
- <dd>None</dd>
- <dt>Optional parameters:</dt>
- <dd>
- <dl>
- <dt><code>form</code></dt>
- <dd>Determines the serialization form for the JSON-LD document. Valid
- values include; <code>compacted</code>, <code>expanded</code>,
- <code>framed</code>, and <code>normalized</code>. Other values are
- allowed, but must be pre-pended with a <code>x-</code> string until
- they are clearly defined by a stable specification. If no form
- is specified in an HTTP request header to a responding application,
- such as a Web server, the application MAY choose any form. If no
- form is specified for a receiving application, the form MUST NOT
- be assumed to take any particular form.</dd>
- <div class="issue">It is currently <a href="https://github.com/json-ld/json-ld.org/issues/14"> being discussed to remove form=framed</a> from this specification as there are several issues with it.</div>
- </dl>
- </dd>
- <dt>Encoding considerations:</dt>
- <dd>The same as the <code>application/json</code> MIME media type.</dd>
- <dt>Security considerations:</dt>
- <dd>Since JSON-LD is intended to be a pure data exchange format for
- directed graphs, the serialization SHOULD NOT be passed through a
- code execution mechanism such as JavaScript's <code>eval()</code>
- function. It is RECOMMENDED that a conforming parser does not attempt to
- directly evaluate the JSON-LD serialization and instead purely parse the
- input into a language-native data structure. </dd>
- <dt>Interoperability considerations:</dt>
- <dd>Not Applicable</dd>
- <dt>Published specification:</dt>
- <dd>The <a href="http://json-ld/spec/latest/">JSON-LD</a> specification.</dd>
- <dt>Applications that use this media type:</dt>
- <dd>Any programming environment that requires the exchange of
- directed graphs. Implementations of JSON-LD have been created for
- JavaScript, Python, Ruby, PHP and C++.
- </dd>
- <dt>Additional information:</dt>
- <dd>
- <dl>
- <dt>Magic number(s):</dt>
- <dd>Not Applicable</dd>
- <dt>File extension(s):</dt>
- <dd>.jsonld</dd>
- <dt>Macintosh file type code(s):</dt>
- <dd>TEXT</dd>
- </dl>
- </dd>
- <dt>Person & email address to contact for further information:</dt>
- <dd>Manu Sporny <msporny@digitalbazaar.com></dd>
- <dt>Intended usage:</dt>
- <dd>Common</dd>
- <dt>Restrictions on usage:</dt>
- <dd>None</dd>
- <dt>Author(s):</dt>
- <dd>Manu Sporny, Gregg Kellogg, Dave Longley</dd>
- <dt>Change controller:</dt>
- <dd>W3C</dd>
-</dl>
-
-</section>
-
-<section class="appendix">
-<h1>Acknowledgements</h1>
-
-<p>The editors would like to thank Mark Birbeck, who provided a great deal of
-the initial push behind the JSON-LD work via his work on RDFj,
-Dave Longley, Dave Lehn and Mike Johnson who reviewed, provided feedback, and
-performed several implementations of the specification, and Ian Davis, who
-created RDF/JSON. Thanks also to Nathan Rixham, Bradley P. Allen,
-Kingsley Idehen, Glenn McDonald, Alexandre Passant, Danny Ayers, Ted
-Thibodeau Jr., Olivier Grisel, Niklas Lindström, Markus Lanthaler, and Richard
-Cyganiak for their input on the specification. Another huge thank you goes out
-to Dave Longley who designed many of the algorithms used in this specification,
-including the normalization algorithm which was a monumentally difficult
-design challenge.
-</p>
-</section>
-
-</body>
-</html>
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/spec/latest/json-ld-syntax/index.html Sat Oct 15 19:56:40 2011 -0400
@@ -0,0 +1,4334 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title>JSON-LD 1.0</title>
+<meta http-equiv="content-type" content="text/html; charset=UTF-8">
+<!--
+ === NOTA BENE ===
+ For the three scripts below, if your spec resides on dev.w3 you can check them
+ out in the same tree and use relative links so that they'll work offline,
+ -->
+<script type="text/javascript"
+ src="http://dev.w3.org/2009/dap/ReSpec.js/js/respec.js" class="remove">
+ </script>
+<script type="text/javascript" class="remove">
+
+ var preProc = {
+ apply: function(c) {
+ // extend the bibliography entries
+ berjon.biblio["MICRODATA"] = "Ian Hickson; et al. <a href=\"http://www.w3.org/TR/microdata/\"><cite>Microdata</cite></a> 04 March 2010. W3C Working Draft. URL: <a href=\"http://www.w3.org/TR/microdata/\">http://www.w3.org/TR/microdata/</a> ";
+ berjon.biblio["HTML-RDFA"] = "Manu Sporny; et al. <a href=\"http://www.w3.org/TR/rdfa-in-html/\"><cite>HTML+RDFa</cite></a> 04 March 2010. W3C Working Draft. URL: <a href=\"http://www.w3.org/TR/rdfa-in-html/\">http://www.w3.org/TR/rdfa-in-html/</a> ";
+ berjon.biblio["BCP47"] = "A. Phillips, M. Davis. <a href=\"http://tools.ietf.org/rfc/bcp/bcp47.txt\"><cite>Tags for Identifying Languages</cite></a> September 2009. IETF Best Current Practice. URL: <a href=\"http://tools.ietf.org/rfc/bcp/bcp47.txt\">http://tools.ietf.org/rfc/bcp/bcp47.txt</a>";
+ berjon.biblio["RDF-API"] = "Manu Sporny, Benjamin Adrian, Nathan Rixham; et al. <a href=\"http://www.w3.org/2010/02/rdfa/sources/rdf-api/\"><cite>RDF API</cite></a> Latest. W3C Editor's Draft. URL: <a href=\"http://www.w3.org/2010/02/rdfa/sources/rdf-api/\">http://www.w3.org/2010/02/rdfa/sources/rdf-api/</a>";
+ berjon.biblio["RDF-INTERFACES"] = "Nathan Rixham, Manu Sporny, Benjamin Adrian; et al. <a href=\"http://www.w3.org/2010/02/rdfa/sources/rdf-interfaces/\"><cite>RDF Interfaces</cite></a> Latest. W3C Editor's Draft. URL: <a href=\"http://www.w3.org/2010/02/rdfa/sources/rdf-interfaces/\">http://www.w3.org/2010/02/rdfa/sources/rdf-interfaces/</a>";
+
+ // process the document before anything else is done
+ var refs = document.querySelectorAll('adef') ;
+ for (var i = 0; i < refs.length; i++) {
+ var item = refs[i];
+ var p = item.parentNode ;
+ var con = item.innerHTML ;
+ var sp = document.createElement( 'dfn' ) ;
+ var tit = item.getAttribute('title') ;
+ if (!tit) {
+ tit = con;
+ }
+ sp.className = 'adef' ;
+ sp.title=tit ;
+ sp.innerHTML = con ;
+ p.replaceChild(sp, item) ;
+ }
+ refs = document.querySelectorAll('aref') ;
+ for (var i = 0; i < refs.length; i++) {
+ var item = refs[i];
+ var p = item.parentNode ;
+ var con = item.innerHTML ;
+ var sp = document.createElement( 'a' ) ;
+ sp.className = 'aref' ;
+ sp.setAttribute('title', con);
+ sp.innerHTML = '@'+con ;
+ p.replaceChild(sp, item) ;
+ }
+ // local datatype references
+ refs = document.querySelectorAll('ldtref') ;
+ for (var i = 0; i < refs.length; i++) {
+ var item = refs[i];
+ if (!item) continue ;
+ var p = item.parentNode ;
+ var con = item.innerHTML ;
+ var ref = item.getAttribute('title') ;
+ if (!ref) {
+ ref = item.textContent ;
+ }
+ if (ref) {
+ ref = ref.replace(/\n/g, '_') ;
+ ref = ref.replace(/\s+/g, '_') ;
+ }
+ var sp = document.createElement( 'a' ) ;
+ sp.className = 'datatype';
+ sp.title = ref ;
+ sp.innerHTML = con ;
+ p.replaceChild(sp, item) ;
+ }
+ // external datatype references
+ refs = document.querySelectorAll('dtref') ;
+ for (var i = 0; i < refs.length; i++) {
+ var item = refs[i];
+ if (!item) continue ;
+ var p = item.parentNode ;
+ var con = item.innerHTML ;
+ var ref = item.getAttribute('title') ;
+ if (!ref) {
+ ref = item.textContent ;
+ }
+ if (ref) {
+ ref = ref.replace(/\n/g, '_') ;
+ ref = ref.replace(/\s+/g, '_') ;
+ }
+ var sp = document.createElement( 'a' ) ;
+ sp.className = 'externalDFN';
+ sp.title = ref ;
+ sp.innerHTML = con ;
+ p.replaceChild(sp, item) ;
+ }
+ // now do terms
+ refs = document.querySelectorAll('tdef') ;
+ for (var i = 0; i < refs.length; i++) {
+ var item = refs[i];
+ if (!item) continue ;
+ var p = item.parentNode ;
+ var con = item.innerHTML ;
+ var ref = item.getAttribute('title') ;
+ if (!ref) {
+ ref = item.textContent ;
+ }
+ if (ref) {
+ ref = ref.replace(/\n/g, '_') ;
+ ref = ref.replace(/\s+/g, '_') ;
+ }
+ var sp = document.createElement( 'dfn' ) ;
+ sp.title = ref ;
+ sp.innerHTML = con ;
+ p.replaceChild(sp, item) ;
+ }
+ // now term references
+ refs = document.querySelectorAll('tref') ;
+ for (var i = 0; i < refs.length; i++) {
+ var item = refs[i];
+ if (!item) continue ;
+ var p = item.parentNode ;
+ var con = item.innerHTML ;
+ var ref = item.getAttribute('title') ;
+ if (!ref) {
+ ref = item.textContent ;
+ }
+ if (ref) {
+ ref = ref.replace(/\n/g, '_') ;
+ ref = ref.replace(/\s+/g, '_') ;
+ }
+
+ var sp = document.createElement( 'a' ) ;
+ var id = item.textContent ;
+ sp.className = 'tref' ;
+ sp.title = ref ;
+ sp.innerHTML = con ;
+ p.replaceChild(sp, item) ;
+ }
+ }
+ } ;
+
+
+ var respecConfig = {
+ // specification status (e.g. WD, LCWD, NOTE, etc.). If in doubt use ED.
+ specStatus: "unofficial",
+ //publishDate: "2010-04-29",
+ copyrightStart: "2010",
+
+ // the specification's short name, as in http://www.w3.org/TR/short-name/
+ shortName: "json-ld",
+ subtitle: "A Context-based JSON Serialization for Linking Data",
+ // if you wish the publication date to be other than today, set this
+ // publishDate: "2009-08-06",
+
+ // if there is a previously published draft, uncomment this and set its YYYY-MM-DD date
+ // and its maturity status
+ previousPublishDate: "2011-08-17",
+ previousMaturity: "ED",
+ previousDiffURI: "http://json-ld.org/spec/ED/20110817/index.html",
+ diffTool: "http://www.aptest.com/standards/htmldiff/htmldiff.pl",
+
+ // if there a publicly available Editor's Draft, this is the link
+ edDraftURI: "http://json-ld.org/spec/latest/",
+
+ // if this is a LCWD, uncomment and set the end of its review period
+ // lcEnd: "2009-08-05",
+
+ // if you want to have extra CSS, append them to this list
+ // it is recommended that the respec.css stylesheet be kept
+ extraCSS: [
+ "http://dev.w3.org/2009/dap/ReSpec.js/css/respec.css",
+ "spec.css"
+ ],
+
+ // editors, add as many as you like
+ // only "name" is required
+ editors: [
+ { name: "Manu Sporny", url: "http://manu.sporny.org/",
+ company: "Digital Bazaar", companyURL: "http://digitalbazaar.com/" },
+ { name: "Gregg Kellogg", url: "http://greggkellogg.net/",
+ company: "Kellogg Associates" },
+ { name: "Dave Longley", url: "http://digitalbazaar.com/",
+ company: "Digital Bazaar", companyURL: "http://digitalbazaar.com/"}
+ ],
+
+ // authors, add as many as you like.
+ // This is optional, uncomment if you have authors as well as editors.
+ // only "name" is required. Same format as editors.
+
+ authors: [
+ { name: "Manu Sporny", url: "http://digitalbazaar.com/",
+ company: "Digital Bazaar", companyURL: "http://digitalbazaar.com/" },
+ { name: "Gregg Kellogg", url: "http://greggkellogg.net/",
+ company: "Kellogg Associates" },
+ { name: "Dave Longley", url: "http://digitalbazaar.com/",
+ company: "Digital Bazaar", companyURL: "http://digitalbazaar.com/"},
+ { name: "Mark Birbeck", url: "http://webbackplane.com/",
+ company: "Backplane Ltd.", companyURL: "http://webbackplane.com/" },
+ ],
+
+ // name of the WG
+ wg: "Linking Data in JSON Community Group",
+
+ // URI of the public WG page
+ wgURI: "http://json-ld.org/",
+
+ // name (with the @w3c.org) of the public mailing to which comments are due
+ wgPublicList: "public-linked-json@w3c.org",
+
+ // URI of the patent status for this WG, for Rec-track documents
+ // !!!! IMPORTANT !!!!
+ // This is important for Rec-track documents, do not copy a patent URI from a random
+ // document unless you know what you're doing. If in doubt ask your friendly neighbourhood
+ // Team Contact.
+ wgPatentURI: "",
+ maxTocLevel: 4,
+ preProcess: [ preProc ],
+ alternateFormats: [ {uri: "diff-20110817.html", label: "diff to previous version"} ],
+ };
+
+ function updateExample(doc, content) {
+ // perform transformations to make it render and prettier
+ content = content.replace(/<!--/, '');
+ content = content.replace(/-->/, '');
+ content = doc._esc(content);
+ content = content.replace(/\*\*\*\*([^*]*)\*\*\*\*/g, '<span class="diff">$1</span>') ;
+ return content ;
+ }
+
+ function updateDTD(doc, content) {
+ // perform transformations to
+ // make it render and prettier
+ content = '<pre class="dtd">' + doc._esc(content) + '</pre>';
+ content = content.replace(/!ENTITY % ([^ \t\r\n]*)/g, '!ENTITY <span class="entity">% $1</span>');
+ content = content.replace(/!ELEMENT ([^ \t$]*)/mg, '!ELEMENT <span class="element">$1</span>');
+ return content;
+ }
+
+ function updateSchema(doc, content) {
+ // perform transformations to
+ // make it render and prettier
+ content = '<pre class="dtd">' + doc._esc(content) + '</pre>';
+ content = content.replace(/<xs:element\s+name="([^&]*)"/g, '<xs:element name="<span class="element" id="schema_element_$1">$1</span>"') ;
+ return content;
+ }
+
+ function updateTTL(doc, content) {
+ // perform transformations to
+ // make it render and prettier
+ content = '<pre class="sh_sourceCode">' + doc._esc(content) + '</pre>';
+ content = content.replace(/@prefix/g, '<span class="sh_keyword">@prefix</span>');
+ return content;
+ }
+ </script>
+<style>
+.diff { font-weight:bold; color:#0a3; }
+ol.algorithm.update { margin-left: 2em; }
+ol.algorithm.update>li { list-style-type: none; }
+ol.algorithm.update>li>span.list-number {
+ display:block;
+ float: left;
+ margin-left: -3.5em;
+}
+</style>
+</head>
+
+<body>
+<section id="abstract">
+<p>
+JSON [[!RFC4627]] has proven to be a highly useful object serialization and
+messaging format. In an attempt to harmonize the representation of Linked Data
+in JSON, this specification outlines a common JSON representation format for
+expressing directed graphs; mixing both Linked Data and non-Linked Data in
+a single document.
+</p>
+</section>
+
+<section id='sotd'>
+<p>This document is an experimental work in progress.</p>
+<!-- <p>
+This document has been reviewed by W3C Members, by software
+developers, and by other W3C groups and interested parties, and is
+endorsed by the Director as a W3C Recommendation. It is a stable
+document and may be used as reference material or cited from another
+document. W3C's role in making the Recommendation is to draw attention
+to the specification and to promote its widespread deployment. This
+enhances the functionality and interoperability of the Web.
+</p> -->
+</section>
+
+<section>
+<h1>Introduction</h1>
+
+<p>
+JSON, as specified in [[!RFC4627]], is a simple language for representing
+data on the Web. Linked Data is a technique for creating a graph of interlinked data across
+different
+documents or Web sites. Data entities are described using <tref>IRI</tref>s,
+which are typically dereferencable and thus may be used to find more
+information about an entity, creating a "Web of Knowledge". JSON-LD is intended to be a simple
+publishing method for expressing not only Linked Data in JSON, but also for adding
+semantics to existing JSON.
+</p>
+
+<p>
+JSON-LD is designed as a light-weight syntax that can be used to express
+Linked Data. It is primarily intended to be a way to use Linked Data
+in Javascript and other Web-based programming environments. It is also
+useful when building interoperable Web services and when storing Linked
+Data in JSON-based document storage engines. It is practical and designed
+to be as simple as possible, utilizing the large number of JSON parsers
+and libraries available today. It is designed to be able to
+express key-value pairs, RDF data, RDFa [[RDFA-CORE]] data, Microformats
+[[MICROFORMATS]] data, and Microdata [[MICRODATA]]. That is, it supports
+every major Web-based structured data model in use today.
+</p>
+
+<p>
+The syntax does not necessarily require applications to change their JSON, but
+allows to easily add meaning by adding context in a way that is either in-band or
+out-of-band. The syntax is designed to not disturb already deployed systems
+running on JSON, but provide a smooth upgrade path from JSON to JSON with
+added semantics. Finally, the format is intended to be easy to parse, efficient to
+generate, convertible to RDF in one pass, and require a very small memory footprint
+in order to operate.
+</p>
+
+<section>
+<h2>How to Read this Document</h2>
+
+<p>
+This document is a detailed specification for a serialization of Linked
+Data in JSON. The document is primarily intended for the following audiences:
+</p>
+
+<ul>
+ <li>Web developers that want to understand the design decisions and
+ language syntax for JSON-LD.</li>
+ <li>Software developers that want to encode Microformats, RDFa, or Microdata
+ in a way that is cross-language compatible via JSON.</li>
+ <li>Software developers that want to implement processors and APIs for
+ JSON-LD.</li>
+</ul>
+
+<p>
+To understand the basics in this specification you must first be familiar with
+JSON, which is detailed in [[!RFC4627]]. To understand the API and how it is
+intended to operate in a programming environment, it is useful to have working
+knowledge of the JavaScript programming language [[ECMA-262]] and
+WebIDL [[!WEBIDL]]. To understand how JSON-LD maps to RDF, it is helpful to be
+familiar with the basic RDF concepts [[!RDF-CONCEPTS]].</p>
+
+<p>
+ Examples may contain references to existing vocabularies and use <tref>prefix</tref>es to refer to Web Vocabularies. The following is a list of all vocabularies and their <tref>prefix</tref> abbreviations, as used in this document:
+</p>
+<ul>
+ <li>The <a href="http://purl.org/dc/terms/">Dublin Core</a>
+ vocabulary (abbreviation: <code>dc</code>, e.g., <code>dc:title</code>)</li>
+ <li>The <a href="http://xmlns.com/foaf/0.1/">Friend of a Friend</a>
+ vocabulary (abbreviation: <code>foaf</code>, e.g., <code>foaf:knows</code>)</li>
+ <li>The <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#">RDF</a>
+ vocabulary (abbreviation: <code>rdf</code>, e.g., <code>rdf:type</code>)</li>
+ <li>The <a href="http://www.w3.org/2001/XMLSchema#">XSD</a>
+ vocabulary (abbreviation: <code>xsd</code>, e.g., <code>xsd:integer</code>)</li>
+</ul>
+
+<p>
+ JSON [[RFC4627]] defines several terms which are used throughout this document:
+ <dl>
+ <dt><tdef>JSON Object</tdef></dt><dd>
+ An object structure is represented as a pair of curly brackets surrounding zero or
+ more name/value pairs (or members). A name is a <tref>string</tref>. A single colon comes after
+ each name, separating the name from the value. A single comma separates a value
+ from a following name. The names within an object SHOULD be unique.
+ </dd>
+ <dt><tdef>array</tdef></dt>
+ <dd>
+ An array is an ordered collection of values. An array structure is represented as square brackets surrounding zero or more values (or elements). Elements are separated by commas. Within JSON-LD, array order is not preserved by default, unless
+ specific markup is provided (see <a href="#lists">Lists</a>). This is because the basic data model of JSON-LD
+ is a directed <tref>graph</tref>, which is inherently unordered.
+ </dd>
+ <dt><tdef>string</tdef></dt><dd>
+ A string is a sequence of zero or more Unicode characters, wrapped in double quotes, using backslash escapes. A
+ character is represented as a single character string.
+ </dd>
+ <dt><tdef>number</tdef></dt>
+ <dd>
+ A number is is similar to that used in most programming languages, except that the octal and hexadecimal formats are not used and that leading zeros are not allowed.</dd>
+ <dt><tdef>true</tdef> and <tdef>false</tdef></dt><dd>
+ Boolean values.
+ </dd>
+ <dt><tdef>null</tdef></dt><dd>
+ The use of the <em>null</em> value is undefined within JSON-LD.
+ <div class="issue">Supporting <em>null</em> in JSON-LD might have a number of advantages and should be evaluated. This is currently an <a href="https://github.com/json-ld/json-ld.org/issues/11">open issue</a>.</div>
+ </dd>
+ </dl>
+</p>
+</section>
+
+<section>
+<h2>Contributing</h2>
+
+<p>There are a number of ways that one may participate in the development of
+this specification:</p>
+
+<ul>
+<li>Technical discussion typically occurs on the public mailing list:
+<a href="http://lists.w3.org/Archives/Public/public-linked-json/">public-linked-json@w3.org</a>
+</li>
+
+<li><a href="http://json-ld.org/minutes/">Public teleconferences</a> are held
+on Tuesdays at 1500UTC on the second and fourth week of each month.
+</li>
+
+<li>Specification bugs and issues should be reported in the
+<a href="https://github.com/json-ld/json-ld.org/issues">issue tracker</a>.</li>
+
+<li><a href="https://github.com/json-ld/json-ld.org/tree/master/spec">Source code</a> for the
+specification can be found on Github.</li>
+
+<li>The <a href="http://webchat.freenode.net/?channels=#json-ld">#json-ld</a>
+IRC channel is available for real-time discussion on irc.freenode.net.</li>
+</ul>
+
+</section>
+
+</section>
+
+<section>
+<h1>Design</h1>
+
+<p>The following section outlines the design goals and rationale behind the
+JSON-LD markup language.
+</p>
+
+<section>
+<h2>Goals and Rationale</h2>
+
+<p>
+A number of design considerations were explored during the creation of this
+markup language:
+</p>
+
+<dl>
+ <dt>Simplicity</dt>
+ <dd>Developers need only know JSON and three keywords to use the basic
+ functionality in JSON-LD. No extra processors or software libraries are
+ necessary to use JSON-LD in its most basic form. The language attempts to
+ ensure that developers have an easy learning curve.</dd>
+ <dt>Compatibility</dt>
+ <dd>The JSON-LD markup must be 100% compatible with JSON. This ensures that
+ all of the standard JSON libraries work seamlessly with JSON-LD documents.</dd>
+ <dt>Expressiveness</dt>
+ <dd>The syntax must be able to express directed graphs, which have been proven
+ to be able to simply express almost every real world data model.</dd>
+ <dt>Terseness</dt>
+ <dd>The JSON-LD syntax must be very terse and human readable, requiring as
+ little as possible effort from the developer.</dd>
+ <!--<dt>Pragmatism</dt>
+ <dd>Mixing the expression of pure Linked Data with data that is not
+ linked was an approach that was driven by pragmatism. JSON-LD attempts to be
+ more practical than theoretical in its approach to Linked Data.</dd>-->
+ <dt>Zero Edits, most of the time</dt>
+ <dd>JSON-LD provides a mechanism that allows developers to specify
+ context in a way that is out-of-band. This allows organizations that have
+ already deployed large JSON-based infrastructure to add meaning to their
+ JSON documents in a way that is not disruptive to their day-to-day operations and is
+ transparent to their current customers. At times, mapping JSON to
+ a graph representation can become difficult. In these instances, rather than
+ having JSON-LD support esoteric markup, we chose not to support the use case
+ and support a simplified syntax instead. So, while Zero Edits is a goal,
+ it is not always possible without adding great complexity to the language.
+ </dd>
+ <dt>One-pass Conversion to RDF</dt>
+ <dd>JSON-LD supports one-pass conversion to RDF with a very small memory footprint.</dd>
+</dl>
+</section>
+
+<section>
+<h2>Linked Data</h2>
+<p>
+The following definition for <tref>Linked Data</tref> is the one that will
+be used for this specification.
+</p>
+<ol>
+ <li><tdef>Linked Data</tdef> is a set of documents, each containing a representation of a linked data graph.</li>
+ <li>A <tdef>linked data graph</tdef> is an unordered labeled directed graph, where nodes are <tref>subject</tref>s or <tref>object</tref>s, and edges are properties.</li>
+ <li>A <tdef>subject</tdef> is any node in a <tref>linked data graph</tref> with at least one outgoing edge.</li>
+ <li>A <tref>subject</tref> SHOULD be labeled with an <tref>IRI</tref> (an Internationalized Resource Identifier as described in [[!RFC3987]]).</li>
+ <li>An <tdef>object</tdef> is a node in a <tref>linked data graph</tref> with at least one incoming edge.</li>
+ <li>An <tref>object</tref> MAY be labeled with an <tref>IRI</tref>.</li>
+ <li>An object MAY be a <tdef>subject</tdef> and <tref>object</tref> at the same time.</li>
+ <li>A <tdef>property</tdef> is an edge of the <tref>linked data graph</tref>.</li>
+ <li>A <tref>property</tref> SHOULD be labeled with an <tref>IRI</tref>.</li>
+ <li>An <tref>IRI</tref> that is a label in a <tref>linked data graph</tref> SHOULD be dereferencable to a <tref>Linked Data</tref> document describing the labeled <tref>subject</tref>, <tref>object</tref> or <tref>property</tref>.</li>
+ <li>A <tdef>literal</tdef> is an <tref>object</tref> with a label that is not an <tref>IRI</tref></li>
+</ol>
+
+<p>
+Note that the definition for <tref>Linked Data</tref> above is silent on the
+topic of unlabeled nodes. Unlabeled nodes are not considered
+<tref>Linked Data</tref>. However, this specification allows for the expression
+of unlabled nodes, as most graph-based data sets on the Web contain a number
+of associated nodes that are not named and thus are not directly
+de-referenceable.
+</p>
+</section>
+
+<section>
+<h2>Linking Data</h2>
+
+<p>
+An Internationalized Resource Identifier
+(<tdef><abbr title="Internationalized Resource Identifier">IRI</abbr></tdef>),
+as described in [[!RFC3987]], is a mechanism for representing unique
+identifiers on the web. In <tref>Linked Data</tref>, an IRI is commonly
+used for expressing a <tref>subject</tref>, a <tref>property</tref> or an
+<tref>object</tref>.
+</p>
+
+<p>JSON-LD defines a mechanism to map JSON terms, i.e., keys and values, to IRIs. This does not mean
+that JSON-LD requires every key or value to be an IRI, but rather ensures that
+keys and values can be mapped to IRIs if the developer desires to transform
+their data into Linked Data. There are a few techniques that can ensure
+that developers will generate good Linked Data for the Web. JSON-LD
+formalizes those techniques.
+</p>
+
+<p>We will be using the following JSON markup as the example for the
+rest of this section:
+</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "name": "Manu Sporny",
+ "homepage": "http://manu.sporny.org/",
+ "avatar": "http://twitter.com/account/profile_image/manusporny"
+}
+-->
+</pre>
+</section>
+
+<section>
+<h3>The Context</h3>
+
+<p>In JSON-LD, a context is used to map <tref>term</tref>s, i.e., keys and values
+ in an JSON document, to
+ <tref>IRI</tref>s. A <tdef>term</tdef> is a short word that MAY be expanded
+to an <tref>IRI</tref>. The Web uses IRIs for unambiguous identification. The
+idea is that these <tref>term</tref>s mean something that may be of use to
+other developers and that it is useful to give them an unambiguous identifier.
+That is, it is useful for <tref>term</tref>s to expand to IRIs so that
+developers don't accidentally step on each other's Web Vocabulary terms.
+For example, the term <code>name</code> may map directly to the IRI
+<code>http://xmlns.com/foaf/0.1/name</code>. This allows JSON-LD documents to
+be constructed using the common JSON practice of simple name/value pairs while
+ensuring that the data is useful outside of the page, API or database in which it
+resides.
+</p>
+
+<p>These Linked Data <tref>term</tref>s are typically collected in a context document that would look something like this:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "name": "http://xmlns.com/foaf/0.1/name",
+ "homepage": "http://xmlns.com/foaf/0.1/homepage",
+ "avatar": "http://xmlns.com/foaf/0.1/avatar"
+}
+-->
+</pre>
+
+<p>This context document can then be used in an JSON-LD document by adding a single line. The JSON markup as shown in the previous section could be changed as follows to link to the context document:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ ****"@context": "http://example.org/json-ld-contexts/person",****
+ "name": "Manu Sporny",
+ "homepage": "http://manu.sporny.org/",
+ "avatar": "http://twitter.com/account/profile_image/manusporny"
+}
+-->
+</pre>
+
+<p>The addition above transforms the previous JSON document into a JSON document
+with added semantics because the <code>@context</code> specifies how the
+<strong>name</strong>, <strong>homepage</strong>, and <strong>avatar</strong>
+terms map to IRIs.
+Mapping those keys to IRIs gives the data global context. If two
+developers use the same IRI to describe a property, they are more than likely
+expressing the same concept. This allows both developers to re-use each others
+data without having to agree to how their data will inter-operate on a
+site-by-site basis. Contexts may also contain datatype information
+for certain <tref>term</tref>s as well as other processing instructions for
+the JSON-LD processor.</p>
+<p>Contexts may be specified in-line. This ensures that JSON-LD documents
+can be processed when a JSON-LD processor does not have access to the Web.</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ ****"@context": {
+ "name": "http://xmlns.com/foaf/0.1/name",
+ "homepage": "http://xmlns.com/foaf/0.1/homepage",
+ "avatar": "http://xmlns.com/foaf/0.1/avatar"
+ },****
+ "name": "Manu Sporny",
+ "homepage": "http://manu.sporny.org/",
+ "avatar": "http://twitter.com/account/profile_image/manusporny"
+}
+-->
+</pre>
+
+<p>JSON-LD strives to ensure that developers don't have to change the JSON
+ that is going into and being returned from their Web APIs. This means
+ that developers can also specify a context for JSON data in an out-of-band
+ fashion. This is described later in this document. </p>
+
+<p>
+ JSON-LD uses a special type of machine-readable document called a
+ <tdef>Web Vocabulary</tdef> to define <tref>term</tref>s that are then used
+ to describe concepts and "things" in the world.
+ Typically, these Web Vocabulary documents have <tref>prefix</tref>es associated
+ with them and contain a number of <tref>term</tref> declarations. A
+ <tdef>prefix</tdef>, like a <tref>term</tref>, is a short word that expands
+ to a Web Vocabulary base IRI. <tref>Prefix</tref>es are helpful when a developer
+ wants to mix multiple vocabularies together in a context, but does not want
+ to go to the trouble of defining every single term in every single vocabulary.
+ Some Web Vocabularies may have dozens of terms defined. If a developer wants to use
+ 3-4 different vocabularies, the number of terms that
+ would have to be declared in a single context could become quite large. To
+ reduce the number of different terms that must be defined, JSON-LD also allows
+ prefixes to be used to compact IRIs.
+<p>
+
+<p>For example, the IRI <code>http://xmlns.com/foaf/0.1/</code>
+specifies a <tref>Web Vocabulary</tref> which may be represented using the
+<code>foaf</code> <tref>prefix</tref>. The <code>foaf</code> Web Vocabulary
+contains a term called <strong>name</strong>. If you join the
+<code>foaf</code> <tref>prefix</tref> with the <strong>name</strong> suffix,
+you can build a compact IRI that will expand out into an absolute IRI for the
+<code>http://xmlns.com/foaf/0.1/name</code> vocabulary term.
+That is, the compact IRI, or short-form, is <code>foaf:name</code> and the
+expanded-form is <code>http://xmlns.com/foaf/0.1/name</code>. This vocabulary
+term is used to specify a person's name.
+</p>
+
+<p>Developers, and machines, are able to use this IRI (plugging it
+directly into a web browser, for instance) to go to the term and get a
+definition of what the term means. Much like we can use <a href="http://wordnet.princeton.edu/">WordNet</a> today to
+see the definition
+of words in the English language. Developers and machines need the same sort of
+definition of terms. IRIs provide a way to ensure that these terms
+are unambiguous.
+</p>
+
+<p>The context provides a collection of vocabulary <tref>term</tref>s and
+<tref>prefix</tref>es that can be used to expand JSON keys and values into
+<tref>IRI</tref>s.</p>
+
+<p class="note">To ensure the best possible performance, it is a best practice to
+put the context definition at the top of the JSON-LD document. If it isn't listed
+first, processors have to save each key-value pair until the context is processed.
+This creates a memory and complexity burden for one-pass processors.</p>
+
+</section>
+
+<section>
+<h3>From JSON to JSON-LD</h3>
+
+<p>If a set of terms such as, <strong>name</strong>, <strong>homepage</strong>,
+and <strong>avatar</strong>,
+are defined in a context, and that context is used to resolve the
+names in JSON objects, machines are able to automatically expand the terms to
+something meaningful and unambiguous, like this:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "****http://xmlns.com/foaf/0.1/name****": "Manu Sporny",
+ "****http://xmlns.com/foaf/0.1/homepage****": "http://manu.sporny.org"
+ "****http://rdfs.org/sioc/ns#avatar****": "http://twitter.com/account/profile_image/manusporny"
+}
+ -->
+</pre>
+
+<p>Doing this allows JSON to be unambiguously machine-readable without
+requiring developers to drastically change their workflow.</p>
+<p class="note">Please note that this JSON-LD document doesn't define the
+subject and will thus result in an unlabeled or blank node.</p>
+
+</section>
+
+</section>
+
+</section>
+
+<section>
+<h1>Basic Concepts</h1>
+
+<p>JSON-LD is designed to ensure that Linked Data concepts can be marked
+up in a way that is simple to understand and author by Web developers. In many
+cases, regular JSON markup can become Linked Data with the simple addition
+of a context. As more JSON-LD features are used, more semantics are added
+to the JSON markup.</p>
+
+<section>
+<h2>IRIs</h2>
+
+<p>Expressing IRIs are fundamental to Linked Data as that is how most
+<tref>subject</tref>s and many <tref>object</tref> are named. IRIs can be
+expressed in a variety of different ways in JSON-LD.</p>
+
+<ol>
+ <li>In general, <tref>term</tref>s in the key position in
+ a <tref>JSON object</tref> that have a mapping to an IRI or another key in the context are
+ expanded to an IRI by JSON-LD processors. There are special rules for
+ processing keys in <code>@context</code> and when dealing with keys that
+ start with the <code>@subject</code> character.</li>
+ <li>An IRI is generated for the value specified using <code>@subject</code>,
+ if it is a <tref>string</tref>.</li>
+ <li>An IRI is generated for the value specified using <code>@type</code>.</li>
+ <li>An IRI is generated for the value specified using the <code>@iri</code>
+ keyword.</li>
+ <li>An IRI is generated when there are <code>@coerce</code> rules in
+ effect for a key named <code>@iri</code>.</li>
+</ol>
+
+<p>IRIs can be expressed directly in the key position like so:
+</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+...
+ "****http://xmlns.com/foaf/0.1/name****": "Manu Sporny",
+...
+}
+-->
+</pre>
+
+<p>In the example above, the key
+<code>http://xmlns.com/foaf/0.1/name</code> is interpreted as an IRI, as
+opposed to being interpreted as a string.</p>
+
+<p>Term expansion occurs for IRIs if a term is defined within the
+<tref>active context</tref>:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "****@context****": {"****name****": "****http://xmlns.com/foaf/0.1/name****"},
+...
+ "****name****": "Manu Sporny",
+...
+}
+-->
+</pre>
+
+<p><tref>Prefix</tref>es are expanded when used in keys:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "****@context****": {"****foaf****": "****http://xmlns.com/foaf/0.1/****"},
+...
+ "****foaf:name****": "Manu Sporny",
+...
+}
+-->
+</pre>
+
+<p><code>foaf:name</code> above will automatically expand out to the IRI
+<code>http://xmlns.com/foaf/0.1/name</code>.</p>
+
+<p>An IRI is generated when a value is associated with a key using
+the <code>@iri</code> keyword:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+...
+ "homepage": { "****@iri****": "http://manu.sporny.org" }
+...
+}
+-->
+</pre>
+
+<p>If type coercion rules are specified in the <code>@context</code> for
+a particular vocabulary term, an IRI is generated:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{****
+ "@context":
+ {
+ ...
+ "@coerce":
+ {
+ "@iri": "homepage"
+ }
+ }****
+...
+ "homepage": "http://manu.sporny.org/",
+...
+}
+-->
+</pre>
+
+<p>Even though the value <code>http://manu.sporny.org/</code> is a <tref>string</tref>,
+the type coercion rules will transform the value into an IRI when processed
+by a JSON-LD Processor</p>
+
+</section>
+
+<section>
+<h2>Identifying the Subject</h2>
+
+<p>
+ To be able to externally reference nodes, it is important that each node has an unambiguous identifier.
+ <tref>IRI</tref>s are a fundamental concept of Linked Data, and nodes should have a de-referencable
+ identifier used to name and locate them. For nodes to be truely linked, de-referencing the identifier
+ should result in a representation of that node. Associating an IRI with a node tells an application
+ that the returned document contains a description of the node requested.
+</p>
+<p>
+ JSON-LD documents may also contain descriptions of other nodes, so it is necessary to be able to
+ uniquely identify each node which may be externally referenced.
+</p>
+<p>A <tref>subject</tref>
+ of an object in JSON is declared using the <code>@subject</code> key. The subject is the
+first piece of information needed by the JSON-LD processor in order to
+create the (subject, property, object) tuple, also known as a triple.</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+...
+ "****@subject****": "****http://example.org/people#joebob****",
+...
+}
+-->
+</pre>
+
+<p>The example above would set the subject to the IRI
+<code>http://example.org/people#joebob</code>.
+</p>
+
+<p class="note">To ensure the best possible performance, it is a best practice to
+put the <code>@subject</code> key before other key-value pairs in an object. If
+it isn't listed first, processors have to save each key-value pair until
+<code>@subject</code> is processed before they can create valid triples. This
+creates a memory and complexity burden for one-pass processors.</p>
+
+</section>
+
+<section>
+<h2>Specifying the Type</h2>
+
+<p>The type of a particular subject can be specified using the
+<code>@type</code> key. Specifying the type in this way will generate a
+triple of the form (subject, type, type-iri).</p>
+
+<p>To be Linked Data, types MUST be uniquely identified by an
+ <tref>IRI</tref>.</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+...
+ "@subject": "http://example.org/people#joebob",
+ "****@type****": "****http://xmlns.com/foaf/0.1/Person****",
+...
+}
+-->
+</pre>
+
+<p>The example above would generate the following triple if the JSON-LD
+document is mapped to RDF (in N-Triples notation):</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+<http://example.org/people#joebob>
+ <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
+ <http://xmlns.com/foaf/0.1/Person> .
+-->
+</pre>
+
+</section>
+
+<section>
+<h2>Strings</h2>
+
+<p>Regular text strings, also referred to as <tdef>plain literal</tdef>s, are
+easily expressed using regular JSON <tref>string</tref>s.</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+...
+ "name": "****Mark Birbeck****",
+...
+}
+ -->
+</pre>
+
+</section>
+
+<section>
+<h2>String Internationalization</h2>
+
+<p>JSON-LD makes an assumption that strings with associated language encoding
+information are not very common when used in JavaScript and Web Services.
+Thus, it takes a little more effort to express strings with associated
+language information.</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+...
+ "name": ****
+ {
+ "@literal": "花澄",
+ "@language": "ja"
+ }****
+...
+}
+-->
+</pre>
+
+<p>The example above would generate a <tref>plain literal</tref> for
+<em>花澄</em> and associate the <code>ja</code> language code with the triple
+that is generated. Languages MUST be expressed in [[!BCP47]] format.</p>
+
+</section>
+
+<section>
+<h2>Datatypes</h2>
+
+<p>
+ A value with an associated datatype, also known as a
+ <tdef>typed literal</tdef>, is indicated by associating a literal with
+ an IRI which indicates the literal's datatype. Typed literals may be
+ expressed in JSON-LD in three ways:
+</p>
+
+<ol>
+ <li>By utilizing the <code>@coerce</code> keyword.</li>
+ <li>By utilizing the expanded form for specifying objects.</li>
+ <li>By using a native JSON datatype.</li>
+</ol>
+
+<p>The first example uses the <code>@coerce</code> keyword to express a
+typed literal:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{****
+ "@context":
+ {
+ "modified": "http://purl.org/dc/terms/modified",
+ "dateTime": "http://www.w3.org/2001/XMLSchema#dateTime"
+ "@coerce":
+ {
+ "dateTime": "modified"
+ }
+ }****
+...
+ "modified": "2010-05-29T14:17:39+02:00",
+...
+}
+-->
+</pre>
+
+<p>The second example uses the expanded form for specifying objects:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+...
+ "modified": ****
+ {
+ "@literal": "2010-05-29T14:17:39+02:00",
+ "@datatype": "dateTime"
+ }****
+...
+}
+-->
+</pre>
+
+<p>Both examples above would generate an object with the literal value of
+<code>2010-05-29T14:17:39+02:00</code> and the datatype of
+<code>http://www.w3.org/2001/XMLSchema#dateTime</code>.</p>
+
+<p>The third example uses a built-in native JSON type, a
+ <tref>number</tref>, to express a datatype:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+...
+ "@subject": "http://example.org/people#joebob",
+ "age": ****31****
+...
+}
+-->
+</pre>
+
+<p>The example above would generate the following triple:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+<http://example.org/people#joebob>
+ <http://xmlns.com/foaf/0.1/age>
+ "31"^^<http://www.w3.org/2001/XMLSchema#integer> .
+-->
+</pre>
+
+</section>
+
+<section>
+<h2>Multiple Objects for a Single Property</h2>
+
+<p>A JSON-LD author can express multiple triples in a compact way by using
+<tref>array</tref>s. If a subject has multiple values for the same property, the author
+MAY express each property as an <tref>array</tref>.</p>
+
+<p class="note">In JSON-LD, multiple objects on a property are not ordered. This is because typically graphs
+are not inherently ordered data structures. To see more on creating ordered collections
+in JSON-LD, see <a href="#lists">Lists</a>.
+</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+...
+ "@subject": "http://example.org/people#joebob",
+ "nick": ****["joe", "bob", "jaybee"]****,
+...
+}
+-->
+</pre>
+
+<p>The markup shown above would generate the following triples:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+<http://example.org/people#joebob>
+ <http://xmlns.com/foaf/0.1/nick>
+ "joe" .
+<http://example.org/people#joebob>
+ <http://xmlns.com/foaf/0.1/nick>
+ "bob" .
+<http://example.org/people#joebob>
+ <http://xmlns.com/foaf/0.1/nick>
+ "jaybee" .
+-->
+</pre>
+
+</section>
+
+<section>
+<h2>Multiple Typed Literals for a Single Property</h2>
+
+<p>Multiple <tref>typed literal</tref>s may also be expressed using the expanded
+form for objects:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+...
+ "@subject": "http://example.org/articles/8",
+ "modified": ****
+ [
+ {
+ "@literal": "2010-05-29T14:17:39+02:00",
+ "@datatype": "dateTime"
+ },
+ {
+ "@literal": "2010-05-30T09:21:28-04:00",
+ "@datatype": "dateTime"
+ }
+ ]****
+...
+}
+-->
+</pre>
+
+<p>The markup shown above would generate the following triples:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+<http://example.org/articles/8>
+ <http://purl.org/dc/terms/modified>
+ "2010-05-29T14:17:39+02:00"^^http://www.w3.org/2001/XMLSchema#dateTime .
+<http://example.org/articles/8>
+ <http://purl.org/dc/terms/modified>
+ "2010-05-30T09:21:28-04:00"^^http://www.w3.org/2001/XMLSchema#dateTime .
+-->
+</pre>
+
+</section>
+
+<section>
+<h2>Expansion</h2>
+
+<p>Expansion is the process of taking a JSON-LD document and applying a
+context such that all IRI, datatypes, and literal values are expanded so
+that the context is no longer necessary. JSON-LD document expansion
+is typically used as a part of <a href="#normalization">Framing</a> or
+<a href="#normalization">Normalization</a>.</p>
+
+<p>For example, assume the following JSON-LD input document:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "@context":
+ {
+ "name": "http://xmlns.com/foaf/0.1/name",
+ "homepage": "http://xmlns.com/foaf/0.1/homepage",
+ "@coerce":
+ {
+ "@iri": "homepage"
+ }
+ },
+ "name": "Manu Sporny",
+ "homepage": "http://manu.sporny.org/"
+}
+-->
+</pre>
+
+<p>Running the JSON-LD Expansion algorithm against the JSON-LD input document
+provided above would result in the following output:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "http://xmlns.com/foaf/0.1/name": "Manu Sporny",
+ "http://xmlns.com/foaf/0.1/homepage":
+ {
+ "@iri": "http://manu.sporny.org/"
+ }
+}
+-->
+</pre>
+
+</section>
+
+<section>
+<h2>Compaction</h2>
+
+<p>Compaction is the process of taking a JSON-LD document and applying a
+context such that the most compact form of the document is generated. JSON
+is typically expressed in a very compact, key-value format. That is, full
+IRIs are rarely used as keys. At times, a JSON-LD document may be received
+that is not in its most compact form. JSON-LD, via the API, provides a way
+to compact a JSON-LD document.
+</p>
+
+<p>For example, assume the following JSON-LD input document:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "http://xmlns.com/foaf/0.1/name": "Manu Sporny",
+ "http://xmlns.com/foaf/0.1/homepage":
+ {
+ "@iri": "http://manu.sporny.org/"
+ }
+}
+-->
+</pre>
+
+<p>Additionally, assume the following developer-supplied JSON-LD context:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "name": "http://xmlns.com/foaf/0.1/name",
+ "homepage": "http://xmlns.com/foaf/0.1/homepage",
+ "@coerce":
+ {
+ "@iri": "homepage"
+ }
+}
+-->
+</pre>
+
+<p>Running the JSON-LD Compaction algorithm given the context supplied above
+against the JSON-LD input document provided above would result in the following
+output:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "@context":
+ {
+ "name": "http://xmlns.com/foaf/0.1/name",
+ "homepage": "http://xmlns.com/foaf/0.1/homepage",
+ "@coerce":
+ {
+ "@iri": "homepage"
+ }
+ },
+ "name": "Manu Sporny",
+ "homepage": "http://manu.sporny.org/"
+}
+-->
+</pre>
+
+<p>The compaction algorithm also enables the developer to map any expanded
+format into an application-specific compacted format. While the context
+provided above mapped <code>http://xmlns.com/foaf/0.1/name</code> to
+<strong>name</strong>, it could have also mapped it to any arbitrary string
+provided by the developer.
+</p>
+
+</section>
+
+<section>
+<h2>Framing</h2>
+
+<p>A JSON-LD document is a representation of a directed graph. A single
+directed graph can have many different serializations, each expressing
+exactly the same information. Developers typically work with trees, represented as
+<tref>JSON object</tref>s. While mapping a graph to
+a tree can be done, the layout of the end result must be specified in advance.
+A <tdef>Frame</tdef> can be used by a developer on a JSON-LD document to
+specify a deterministic layout for a graph.
+</p>
+
+<p>Framing is the process of taking a JSON-LD document, which expresses a
+graph of information, and applying a specific graph layout
+(called a <tref>Frame</tref>).
+</p>
+
+<p>The JSON-LD document below expresses a library, a book and a chapter:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "@context": {
+ "Book": "http://example.org/vocab#Book",
+ "Chapter": "http://example.org/vocab#Chapter",
+ "contains": "http://example.org/vocab#contains",
+ "creator": "http://purl.org/dc/terms/creator"
+ "description": "http://purl.org/dc/terms/description"
+ "Library": "http://example.org/vocab#Library",
+ "title": "http://purl.org/dc/terms/title",
+ "@coerce":
+ {
+ "@iri": "contains"
+ },
+ },
+ "@subject":
+ [{
+ "@subject": "http://example.com/library",
+ "@type": "Library",
+ "contains": "http://example.org/library/the-republic"
+ },
+ {
+ "@subject": "http://example.org/library/the-republic",
+ "@type": "Book",
+ "creator": "Plato",
+ "title": "The Republic",
+ "contains": "http://example.org/library/the-republic#introduction"
+ },
+ {
+ "@subject": "http://example.org/library/the-republic#introduction",
+ "@type": "Chapter",
+ "description": "An introductory chapter on The Republic.",
+ "title": "The Introduction"
+ }]
+}-->
+</pre>
+
+<p>Developers typically like to operate on items in a hierarchical, tree-based
+fashion. Ideally, a developer would want the data above sorted into top-level
+libraries, then the books that are contained in each library, and then the
+chapters contained in each book. To achieve that layout, the developer can
+define the following <tref>frame</tref>:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "@context": {
+ "Book": "http://example.org/vocab#Book",
+ "Chapter": "http://example.org/vocab#Chapter",
+ "contains": "http://example.org/vocab#contains",
+ "creator": "http://purl.org/dc/terms/creator"
+ "description": "http://purl.org/dc/terms/description"
+ "Library": "http://example.org/vocab#Library",
+ "title": "http://purl.org/dc/terms/title"
+ },
+ "@type": "Library",
+ "contains": {
+ "@type": "Book",
+ "contains": {
+ "@type": "Chapter"
+ }
+ }
+}
+-->
+</pre>
+
+<p>When the framing algorithm is run against the previously defined
+JSON-LD document, paired with the <tref>frame</tref> above, the following
+JSON-LD document is the end result:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "@context": {
+ "Book": "http://example.org/vocab#Book",
+ "Chapter": "http://example.org/vocab#Chapter",
+ "contains": "http://example.org/vocab#contains",
+ "creator": "http://purl.org/dc/terms/creator"
+ "description": "http://purl.org/dc/terms/description"
+ "Library": "http://example.org/vocab#Library",
+ "title": "http://purl.org/dc/terms/title"
+ },
+ "@subject": "http://example.org/library",
+ "@type": "Library",
+ "contains": {
+ ****"@subject": "http://example.org/library/the-republic",****
+ "@type": "Book",
+ ****"creator": "Plato",****
+ ****"title": "The Republic",****
+ "contains": {
+ ****"@subject": "http://example.org/library/the-republic#introduction",****
+ "@type": "Chapter",
+ ****"description": "An introductory chapter on The Republic.",****
+ ****"title": "The Introduction"****
+ },
+ },
+}
+-->
+</pre>
+
+<p>The JSON-LD framing algorithm allows developers to query by example and
+force a specific tree layout to a JSON-LD document.
+</p>
+
+</section>
+
+</section>
+
+<section>
+<h1>Advanced Concepts</h1>
+
+<p>JSON-LD has a number of features that provide functionality above and beyond
+the core functionality described above. The following sections outline the
+features that are specific to JSON-LD.
+</p>
+
+<section>
+ <h2>Vocabulary Prefixes</h2>
+ <p>
+ Vocabulary terms in Linked Data documents may draw from a number of
+ different Web vocabularies. At times, declaring every single term that
+ a document uses can require the developer to declare tens, if not
+ hundreds of potential vocabulary terms that may be used across an
+ application. This is a concern for at least three reasons; the
+ first is the cognitive load on the developer, the second is
+ the serialized size of the context, the third is future-proofing
+ application contexts. In order to address these issues, the concept of a
+ <tref>prefix</tref> mechanism is introduced.</p>
+ <p>
+ A <tdef>prefix</tdef> is a compact way of expressing a base
+ <tref>IRI</tref> to a <tref>Web Vocabulary</tref>.
+ Generally, these prefixes are used by concatenating the <em>prefix</em> and
+ a <em>term</em> separated by a colon (<code>:</code>).
+ The prefix is a short string that identifies a particular Web vocabulary.
+ For example, the prefix <code>foaf</code> may be used as a short
+ hand for the Friend-of-a-Friend Web Vocabulary, which is identified using
+ the IRI <code>http://xmlns.com/foaf/0.1/</code>. A developer may append any of
+ the FOAF Vocabulary terms to the end of the prefix to specify a short-hand
+ version of the full IRI for the vocabulary term. For example,
+ <code>foaf:name</code> would be expanded out to the IRI
+ <code>http://xmlns.com/foaf/0.1/name</code>. Instead of having to remember
+ and type out the entire IRI, the developer can instead use the prefix in
+ their JSON-LD markup.
+ </p>
+ <p>
+ The ability to use <tref>prefix</tref>es reduces the need for developers
+ to declare every vocabulary term that they intend to use in
+ the JSON-LD context. This reduces document serialization size because
+ every vocabulary term need not be declared in the context.
+ <tref>Prefix</tref> also
+ reduce the cognitive load on the developer. It is far easier to
+ remember <code>foaf:name</code> than it is to remember
+ <code>http://xmlns.com/foaf/0.1/name</code>. The use of prefixes also
+ ensures that a context document does not have to be updated in lock-step
+ with an externally defined <tref>Web Vocabulary</tref>. Without prefixes, a developer
+ would need to keep their application context terms in lock-step with an
+ externally defined Web Vocabulary. Rather, by just declaring the
+ Web Vocabulary prefix, one can use new terms as they're declared
+ without having to update the application's JSON-LD context.
+ </p>
+ <p>Consider the following example:</p>
+ <pre class="example" data-transform="updateExample">
+<!--
+{
+ "@context": {
+ ****"dc": "http://purl.org/dc/elements/1.1/",****
+ ****"ex": "http://example.org/vocab#"****
+ },
+ "@subject": "http://example.org/library",
+ "@type": ****"ex:Library"****,
+ ****"ex:contains"****: {
+ "@subject": "http://example.org/library/the-republic",
+ "@type": ****"ex:Book"****,
+ ****"dc:creator"****: "Plato",
+ ****"dc:title"****: "The Republic",
+ ****"ex:contains"****: {
+ "@subject": "http://example.org/library/the-republic#introduction",
+ "@type": ****"ex:Chapter"****,
+ ****"dc:description"****: "An introductory chapter on The Republic.",
+ ****"dc:title"****: "The Introduction"
+ },
+ },
+}
+-->
+ </pre>
+ <p>
+ In this example, two different vocabularies are referred to using
+ prefixes. Those prefixes are then used as type and property values using
+ the <code>prefix:term</code> notation.
+ </p>
+ <p>
+ Prefixes, also known as CURIEs, are defined more formally in RDFa Core 1.1,
+ <cite><a href="http://www.w3.org/TR/rdfa-core/#s_curies">Section 6
+ "CURIE Syntax Definition"</a></cite> [[RDFA-CORE]].
+ JSON-LD does not support the square-bracketed CURIE syntax as the
+ mechanism is not required to disambiguate IRIs in a JSON-LD document like
+ it is in HTML documents.
+ </p>
+</section>
+
+<section>
+<h2>Automatic Typing</h2>
+
+<p>Since JSON is capable of expressing typed information such as doubles,
+integers, and boolean values. As demonstrated below, JSON-LD utilizes that
+information to create <tref>typed literal</tref>s:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+...
+ // The following two values are automatically converted to a type of xsd:double
+ // and both values are equivalent to each other.
+ "measure:cups": ****5.3****,
+ "measure:cups": ****5.3e0****,
+ // The following value is automatically converted to a type of xsd:double as well
+ "space:astronomicUnits": ****6.5e73****,
+ // The following value should never be converted to a language-native type
+ "measure:stones": ****{ "@literal": "4.8", "@datatype": "xsd:decimal" }****,
+ // This value is automatically converted to having a type of xsd:integer
+ "chem:protons": ****12****,
+ // This value is automatically converted to having a type of xsd:boolean
+ "sensor:active": ****true****,
+...
+}
+-->
+</pre>
+
+<p class="note">When dealing with a number of modern programming languages,
+including JavaScript ECMA-262, there is no distinction between
+<strong>xsd:decimal</strong> and <strong>xsd:double</strong> values. That is,
+the <tref>number</tref> <code>5.3</code> and the <tref>number</tref>
+<code>5.3e0</code> are treated as if they were the same. When converting from
+JSON-LD to a language-native format and back, datatype information is lost in a
+number of these languages. Thus, one could say that <code>5.3</code> is a
+<strong>xsd:decimal</strong> and <code>5.3e0</code> is an
+<strong>xsd:double</strong> in JSON-LD, but when both values are
+converted to a language-native format the datatype difference between the two
+is lost because the machine-level representation will almost always be a
+<strong>double</strong>.
+Implementers should be aware of this potential round-tripping issue between
+<strong>xsd:decimal</strong> and <strong>xsd:double</strong>. Specifically
+objects with a datatype of <strong>xsd:decimal</strong> MUST NOT be converted
+to a language native type.
+</p>
+
+</section>
+
+<section>
+<h2>Type Coercion</h2>
+
+<p>JSON-LD supports the coercion of values to particular data types.
+Type coercion allows someone deploying JSON-LD to coerce the incoming or
+outgoing types to the proper data type based on a mapping of data type IRIs to
+property types. Using type coercion, one may convert simple JSON data to
+properly typed RDF data.</p>
+
+<p>The example below demonstrates how a JSON-LD author can coerce values to
+<tref>plain literal</tref>s, <tref>typed literal</tref>s and IRIs.</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "@context":
+ {
+ "rdf": "http://www.w3.org/1999/02/22-rdf-syntax-ns#",
+ "xsd": "http://www.w3.org/2001/XMLSchema#",
+ "name": "http://xmlns.com/foaf/0.1/name",
+ "age": "http://xmlns.com/foaf/0.1/age",
+ "homepage": "http://xmlns.com/foaf/0.1/homepage",
+**** "@coerce":
+ {
+ "xsd:integer": "age",
+ "@iri": "homepage"
+ }****
+ },
+ "name": "John Smith",
+ "age": ****"41"****,
+ "homepage": ****"http://example.org/home/"****
+}
+-->
+</pre>
+
+<p>The example above would generate the following triples:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+_:bnode1
+ <http://xmlns.com/foaf/0.1/name>
+ "John Smith" .
+_:bnode1
+ <http://xmlns.com/foaf/0.1/age>
+ "41"^^http://www.w3.org/2001/XMLSchema#integer .
+_:bnode1
+ <http://xmlns.com/foaf/0.1/homepage>
+ <http://example.org/home/> .
+-->
+</pre>
+
+</section>
+
+<section>
+ <h2>Chaining</h2>
+ <p>
+ Object <tdef>chaining</tdef> is a JSON-LD feature that allows an author to
+ use the definition of JSON-LD objects as <tref>property</tref> values. This
+ is a commonly used mechanism for creating a parent-child relationship
+ between two <tref>subject</tref>s.
+ </p>
+ <p>The example shows an two subjects related by a property from the first
+ subject:</p>
+
+ <pre class="example" data-transform="updateExample">
+ <!--
+ {
+ ...
+ "name": "Manu Sporny",
+ "****knows****": {
+ "****@type****": "****Person****",
+ "****name****": "****Gregg Kellogg****",
+ }
+ ...
+ }
+ -->
+ </pre>
+
+ <p>
+ An object definition, like the one used above, MAY be used as a
+ JSON value at any point in JSON-LD.
+ </p>
+</section>
+
+<section>
+<h2>Identifying Unlabeled Nodes</h2>
+
+<p>At times, it becomes necessary to be able to express information without
+being able to specify the subject. Typically, this type of node is called
+an unlabeled node or a blank node. In JSON-LD, unlabeled node identifiers are
+automatically created if a subject is not specified using the
+<code>@subject</code> keyword. However, authors may provide identifiers for
+unlabeled nodes by using the special <code>_</code> (underscore)
+<tref>prefix</tref>. This allows to reference the node locally within the
+document but not in an external document.</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+...
+ "@subject": "****_:foo****",
+...
+}
+ -->
+</pre>
+
+<p>The example above would set the subject to <code>_:foo</code>, which can
+then be used later on in the JSON-LD markup to refer back to the
+unlabeled node. This practice, however, is usually frowned upon when
+generating Linked Data. If a developer finds that they refer to the unlabeled
+node more than once, they should consider naming the node using a resolve-able
+IRI.
+</p>
+
+</section>
+
+<section>
+<h2>Aliasing Keywords</h2>
+
+<p>JSON-LD allows all of the syntax keywords, except for <code>@context</code>,
+to be aliased. This feature allows more legacy JSON content to be supported
+by JSON-LD. It also allows developers to design domain-specific implementations
+using only the JSON-LD context.</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "@context":
+ {
+ ****"url": "@subject"****,
+ ****"a": "@type"****,
+ "name": "http://schema.org/name"
+ },
+ "url": "http://example.com/about#gregg",
+ "a": "http://schema.org/Person",
+ "name": "Gregg Kellogg"
+}
+-->
+</pre>
+
+<p>In the example above, the <code>@subject</code> and <code>@type</code>
+keywords have been given the aliases <strong>url</strong> and
+<strong>a</strong>, respectively.
+</p>
+
+</section>
+
+<section>
+<h2>Normalization</h2>
+
+<p>Normalization is the process of taking <tref>JSON-LD input</tref> and
+performing a deterministic transformation on that input that results in a
+<tref>JSON-LD output</tref> that any conforming JSON-LD processor would have
+generated given the same input. The problem is a fairly difficult technical
+problem to solve because it requires a directed graph to be ordered into a
+set of nodes and edges in a deterministic way. This is easy to do when all of
+the nodes have unique names, but very difficult to do when some of the nodes
+are not labeled.
+</p>
+
+<p>Normalization is useful when comparing two graphs against one another,
+when generating a detailed list of differences between two graphs, and
+when generating a cryptographic digital signature for information contained
+in a graph or when generating a hash of the information contained in a graph.
+</p>
+
+<p>The example below is an un-normalized JSON-LD document:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "@context":
+ {
+ "name": "http://xmlns.com/foaf/0.1/name",
+ "homepage": "http://xmlns.com/foaf/0.1/homepage",
+ "xsd": "http://www.w3.org/2001/XMLSchema#",
+ "@coerce":
+ {
+ "@iri": ["homepage"]
+ }
+ },
+ "name": "Manu Sporny",
+ "homepage": "http://manu.sporny.org/"
+}
+-->
+</pre>
+
+<p>The example below is the normalized form of the JSON-LD document above:</p>
+
+<p class="note">Whitespace is used below to aid readability. The normalization
+algorithm for JSON-LD removes all unnecessary whitespace in the fully
+normalized form.</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+[{
+ "@subject":
+ {
+ "@iri": "_:c14n0"
+ },
+ "http://xmlns.com/foaf/0.1/homepage":
+ {
+ "@iri": "http://manu.sporny.org/"
+ },
+ "http://xmlns.com/foaf/0.1/name": "Manu Sporny"
+}]
+-->
+</pre>
+
+<p>Notice how all of the <tref>term</tref>s have been expanded and sorted in
+alphabetical order. Also, notice how the <tref>subject</tref> has been
+labeled with a <tref>blank node identifier</tref>. Normalization ensures that any arbitrary
+graph containing exactly the same information would be normalized to exactly
+the same form shown above.</p>
+
+</section>
+
+</section>
+
+<section>
+<h2>The Application Programming Interface</h2>
+
+<p>This API provides a clean mechanism that enables developers to convert
+JSON-LD data into a a variety of output formats that are easier to work with in
+various programming languages. If a JSON-LD API is provided in a programming
+environment, the entirety of the following API MUST be implemented.
+</p>
+
+<section>
+<h3>JsonLdProcessor</h3>
+<dl title="[NoInterfaceObject] interface JsonLdProcessor" class="idl">
+
+ <dt>object expand()</dt>
+ <dd><a href="#expansion">Expands</a> the given <code>input</code>
+ according to the steps in the
+ <a href="#expansion-algorithm">Expansion Algorithm</a>. The
+ <code>input</code> MUST be copied, expanded and returned if there are
+ no errors. If the expansion fails, an appropriate exception MUST be thrown.
+
+ <dl class="parameters">
+ <dt>object input</dt>
+ <dd>The JSON-LD object to copy and perform the expansion upon.</dd>
+ <dt>object optional? context</dt>
+ <dd>An external context to use additionally to the context embedded in <code>input</code> when expanding the <code>input</code>.</dd>
+ </dl>
+
+ <dl class="exception" title="InvalidContext">
+ <dt>INVALID_SYNTAX</dt>
+ <dd>A general syntax error was detected in the <code>@context</code>.
+ For example, if a <code>@coerce</code> key maps to anything other than
+ a string or an array of strings, this exception would be raised.</dd>
+ <dt>MULTIPLE_DATATYPES</dt>
+ <dd>There is more than one target datatype specified for a single
+ property in the list of coercion rules. This means that the processor
+ does not know what the developer intended for the target datatype for a
+ property.</dd>
+ </dl>
+
+ </dd>
+
+ <dt>object compact()</dt>
+ <dd><a href="#compaction">Compacts</a> the given <code>input</code>
+ according to the steps in the
+ <a href="#compaction-algorithm">Compaction Algorithm</a>. The
+ <code>input</code> MUST be copied, compacted and returned if there are
+ no errors. If the compaction fails, an appropirate exception MUST be
+ thrown.
+ <dl class="parameters">
+ <dt>object input</dt>
+ <dd>The JSON-LD object to perform compaction on.</dd>
+ <dt>object optional? context</dt>
+ <dd>The base context to use when compacting the <code>input</code>.</dd>
+ </dl>
+
+ <dl class="exception" title="InvalidContext">
+ <dt>INVALID_SYNTAX</dt>
+ <dd>A general syntax error was detected in the <code>@context</code>.
+ For example, if a <code>@coerce</code> key maps to anything other than
+ a string or an array of strings, this exception would be raised.</dd>
+ <dt>MULTIPLE_DATATYPES</dt>
+ <dd>There is more than one target datatype specified for a single
+ property in the list of coercion rules. This means that the processor
+ does not know what the developer intended for the target datatype for a
+ property.</dd>
+ </dl>
+
+ <dl class="exception" title="ProcessingError">
+ <dt>LOSSY_COMPACTION</dt>
+ <dd>The compaction would lead to a loss of information, such as a
+ <code>@language</code> value.</dd>
+ <dt>CONFLICTING_DATATYPES</dt>
+ <dd>The target datatype specified in the coercion rule and the
+ datatype for the typed literal do not match.</dd>
+ </dl>
+
+ </dd>
+
+ <dt>object frame()</dt>
+ <dd><a href="#framing">Frames</a> the given <code>input</code>
+ using the <code>frame</code> according to the steps in the
+ <a href="#framing-algorithm">Framing Algorithm</a>. The
+ <code>input</code> is used to build the framed output and is returned if
+ there are no errors. If there are no matches for the frame,
+ <code>null</code> MUST be returned. Exceptions MUST be thrown if there are
+ errors.
+ <dl class="parameters">
+ <dt>object input</dt>
+ <dd>The JSON-LD object to perform framing on.</dd>
+ <dt>object frame</dt>
+ <dd>The frame to use when re-arranging the data.</dd>
+ <dt>object options</dt>
+ <dd>A set of options that will affect the framing algorithm.</dd>
+ </dl>
+
+ <dl class="exception" title="InvalidFrame">
+ <dt>INVALID_SYNTAX</dt>
+ <dd>A frame must be either an object or an array of objects, if the frame
+ is neither of these types, this exception is thrown.</dd>
+ <dt>MULTIPLE_EMBEDS</dt>
+ <dd>A subject IRI was specified in more than one place in the input
+ frame. More than one embed of a given subject IRI is not allowed, and if
+ requested, MUST result in this exception.</dd>
+ </dl>
+
+ </dd>
+
+ <dt>object normalize()</dt>
+ <dd><a href="#normalization">Normalizes</a> the given <code>input</code>
+ according to the steps in the
+ <a href="#normalization-algorithm">Normalization Algorithm</a>. The
+ <code>input</code> MUST be copied, normalized and returned if there are
+ no errors. If the compaction fails, <code>null</code> MUST be returned.
+ <dl class="parameters">
+ <dt>object input</dt>
+ <dd>The JSON-LD object to perform normalization upon.</dd>
+ <dt>object optional? context</dt>
+ <dd>An external context to use additionally to the context embedded in <code>input</code> when expanding the <code>input</code>.</dd>
+ </dl>
+
+ <dl class="exception" title="InvalidContext">
+ <dt>INVALID_SYNTAX</dt>
+ <dd>A general syntax error was detected in the <code>@context</code>.
+ For example, if a <code>@coerce</code> key maps to anything other than
+ a string or an array of strings, this exception would be raised.</dd>
+ <dt>MULTIPLE_DATATYPES</dt>
+ <dd>There is more than one target datatype specified for a single
+ property in the list of coercion rules. This means that the processor
+ does not know what the developer intended for the target datatype for a
+ property.</dd>
+ </dl>
+
+ </dd>
+
+ <dt>object triples()</dt>
+ <dd>Processes the <code>input</code> according to the
+ <a href="#rdf-conversion-algorithm">RDF Conversion Algorithm</a>, calling
+ the provided <code>tripleCallback</code> for each triple generated.
+ <dl class="parameters">
+ <dt>object input</dt>
+ <dd>The JSON-LD object to process when outputting triples.</dd>
+ <dt>JsonLdTripleCallback tripleCallback</dt>
+ <dd>A callback that is called whenever a processing error occurs on
+ the given <code>input</code>.
+ <div class="issue">This callback should be aligned with the
+ RDF API.</div></dd>
+ <dt>object optional? context</dt>
+ <dd>An external context to use additionally to the context embedded in <code>input</code> when expanding the <code>input</code>.</dd>
+ </dl>
+
+ <dl class="exception" title="InvalidContext">
+ <dt>INVALID_SYNTAX</dt>
+ <dd>A general syntax error was detected in the <code>@context</code>.
+ For example, if a <code>@coerce</code> key maps to anything other than
+ a string or an array of strings, this exception would be raised.</dd>
+ <dt>MULTIPLE_DATATYPES</dt>
+ <dd>There is more than one target datatype specified for a single
+ property in the list of coercion rules. This means that the processor
+ does not know what the developer intended for the target datatype for a
+ property.</dd>
+ </dl>
+
+ </dd>
+
+</dl>
+
+</section>
+
+<section>
+<h3>JsonLdTripleCallback</h3>
+<p>The JsonLdTripleCallback is called whenever the processor generates a
+triple during the <code>triple()</code> call.</p>
+
+<dl title="[NoInterfaceObject Callback] interface JsonLdTripleCallback"
+ class="idl">
+
+ <dt>void triple()</dt>
+ <dd>This callback is invoked whenever a triple is generated by the processor.
+ <dl class="parameters">
+ <dt>DOMString subject</dt>
+ <dd>The subject IRI that is associated with the triple.</dd>
+ <dt>DOMString property</dt>
+ <dd>The property IRI that is associated with the triple.</dd>
+ <dt>DOMString objectType</dt>
+ <dd>The type of object that is associated with the triple. Valid values
+ are <code>IRI</code> and <code>literal</code>.</dd>
+ <dt>DOMString object</dt>
+ <dd>The object value associated with the subject and the property.</dd>
+ <dt>DOMString? datatype</dt>
+ <dd>The datatype associated with the object.</dd>
+ <dt>DOMString? language</dt>
+ <dd>The language associated with the object in BCP47 format.</dd>
+ </dl>
+ </dd>
+</dl>
+</section>
+
+
+</section>
+
+<section>
+<h1>Algorithms</h1>
+
+<p>All algorithms described in this section are intended to operate on
+language-native data structures. That is, the serialization to a text-based
+JSON document isn't required as input or output to any of these algorithms and
+language-native data structures MUST be used where applicable.</p>
+
+<section>
+ <h2>Syntax Tokens and Keywords</h2>
+
+ <p>JSON-LD specifies a number of syntax tokens and keywords that are using
+ in all algorithms described in this section:</p>
+
+ <dl>
+ <dt><code>@context</code></dt><dd>Used to set the <tref>local context</tref>.</dd>
+ <dt><code>@base</code></dt><dd>Used to set the base IRI for all object IRIs affected by the <tref>active context</tref>.</dd>
+ <dt><code>@vocab</code></dt><dd>Used to set the base IRI for all property IRIs affected by the <tref>active context</tref>.</dd>
+ <dt><code>@coerce</code></dt><dd>Used to specify type coercion rules.</dd>
+ <dt><code>@literal</code></dt><dd>Used to specify a literal value.</dd>
+ <dt><code>@iri</code></dt><dd>Used to specify an IRI value.</dd>
+ <dt><code>@language</code></dt><dd>Used to specify the language for a literal.</dd>
+ <dt><code>@datatype</code></dt><dd>Used to specify the datatype for a literal.</dd>
+ <dt><code>:</code></dt><dd>The separator for JSON keys and values that use the <tref>prefix</tref> mechanism.</dd>
+ <dt><code>@subject</code></dt><dd>Sets the active subject.</dd>
+ <dt><code>@type</code></dt><dd>Used to set the type of the active subject.</dd>
+ </dl>
+</section>
+
+<section>
+ <h2>Algorithm Terms</h2>
+ <dl>
+ <dt><tdef>initial context</tdef></dt>
+ <dd>
+ a context that is specified to the algorithm before processing begins.
+ </dd>
+ <dt><tdef>active subject</tdef></dt>
+ <dd>
+ the currently active subject that the processor should use when
+ processing.
+ </dd>
+ <dt><tdef>active property</tdef></dt>
+ <dd>
+ the currently active property that the processor should use when
+ processing.
+ </dd>
+ <dt><tdef>active object</tdef></dt>
+ <dd>
+ the currently active object that the processor should use when
+ processing.
+ </dd>
+ <dt><tdef>active context</tdef></dt>
+ <dd>
+ a context that is used to resolve <tref>prefix</tref>es and
+ <tref>term</tref>s while the processing
+ algorithm is running. The <tref>active context</tref> is the context
+ contained within the <tref>processor state</tref>.
+ </dd>
+ <dt><tdef>local context</tdef></dt>
+ <dd>
+ a context that is specified within a <tref>JSON object</tref>,
+ specified via the <code>@context</code> keyword.
+ </dd>
+ <dt><tdef>processor state</tdef></dt>
+ <dd>
+ the <tref>processor state</tref>, which includes the <tref>active
+ context</tref>, <tref>current subject</tref>, and
+ <tref>current property</tref>. The <tref>processor state</tref> is managed
+ as a stack with elements from the previous <tref>processor state</tref>
+ copied into a new <tref>processor state</tref> when entering a new
+ <tref>JSON object</tref>.
+ </dd>
+ <dt><tdef>JSON-LD input</tdef></dt>
+ <dd>
+ The JSON-LD data structure that is provided as input to the algorithm.
+ </dd>
+ <dt><tdef>JSON-LD output</tdef></dt>
+ <dd>
+ The JSON-LD data structure that is produced as output by the algorithm.
+ </dd>
+
+ </dl>
+</section>
+
+<section>
+ <h2 id="context">Context</h2>
+ <p>
+ Processing of JSON-LD data structure is managed recursively.
+ During processing, each rule is applied using information provided by the <tref>active context</tref>.
+ Processing begins by pushing a new <tref>processor state</tref> onto the <tref>processor state</tref> stack and
+ initializing the <tref>active context</tref> with the <tref>initial context</tref>. If a <tref>local context</tref> is encountered,
+ information from the <tref>local context</tref> is merged into the <tref>active context</tref>.
+ </p>
+ <p>
+ The <tref>active context</tref> is used for expanding keys and values of a <tref>JSON object</tref> (or elements
+ of a list (see <span a="#list-processing">List Processing</span>)).
+ </p>
+ <p>
+ A <tref>local context</tref> is identified within a <tref>JSON object</tref> having a key of
+ <code>@context</code> with <tref>string</tref> or a <tref>JSON object</tref> value. When processing a <tref>local
+ context</tref>, special processing rules apply:
+ </p>
+ <ol class="algorithm">
+ <li>Create a new, empty <tref>local context</tref>.</li>
+ <li>
+ If the value is a simple <tref>string</tref>, it MUST have a lexical form of IRI and used to initialize
+ a new JSON document which replaces the value for subsequent processing.
+ </li>
+ <li>If the value is a <tref>JSON object</tref>, perform the following steps:
+ <ol class="algorithm">
+ <li>
+ If the <tref>JSON object</tref> has a <code>@base</code> key, it MUST have a value of a simple
+ <tref>string</tref> with the lexical form of an absolute IRI. Add the base mapping to the <tref>local
+ context</tref>. <p class="issue">Turtle allows @base to be relative. If we did this, we
+ would have to add <a href="#iri-expansion">IRI Expansion</a>.</p>
+ </li>
+ <li>
+ If the <tref>JSON object</tref> has a <code>@vocab</code> key, it MUST have a value of a simple
+ <tref>string</tref> with the lexical form of an absolute IRI. Add the vocabulary mapping to the
+ <tref>local context</tref> after performing <a href="#iri-expansion">IRI Expansion</a> on
+ the associated value.
+ </li>
+ <li>
+ If the <tref>JSON object</tref> has a <code>@coerce</code> key, it MUST have a value of a
+ <tref>JSON object</tref>. Add the <code>@coerce</code> mapping to the <tref>local context</tref>
+ performing <a href="#iri-expansion">IRI Expansion</a> on the associated value(s).
+ </li>
+ <li>
+ Otherwise, the key MUST have the lexical form of <cite><a
+ href="http://www.w3.org/TR/2009/REC-xml-names-20091208/#NT-NCName">NCName</a></cite> and
+ MUST have the value of a simple <tref>string</tref> with the lexical form of IRI. Merge the key-value
+ pair into the <tref>local context</tref>.
+ </li>
+ </ol>
+ </li>
+ <li>
+ Merge the of <tref>local context</tref>'s <code>@coerce</code> mapping into the
+ <tref>active context</tref>'s <code>@coerce</code> mapping as described <a href="#coerce">below</a>.
+ </li>
+ <li>
+ Merge all entries other than the <code>@coerce</code> mapping from the <tref>local context</tref> to the
+ <tref>active context</tref> overwriting any duplicate values.
+ </li>
+ </ol>
+
+ <section>
+ <h3>Coerce</h3>
+ <p>
+ Map each key-value pair in the <tref>local context</tref>'s
+ <code>@coerce</code> mapping into the <tref>active context</tref>'s
+ <code>@coerce</code> mapping, overwriting any duplicate values in
+ the <tref>active context</tref>'s <code>@coerce</code> mapping.
+ The <code>@coerce</code> mapping has either a single
+ <code>prefix:term</code> value, a single <tref>term</tref> value or an
+ <tref>array</tref> of <code>prefix:term</code> or <tref>term</tref> values.
+ When merging with an existing mapping in the <tref>active context</tref>,
+ map all <tref>prefix</tref> and <tref>term</tref> values to
+ <tref>array</tref> form and replace with the union of the value from
+ the <tref>local context</tref> and the value of the
+ <tref>active context</tref>. If the result is an <tref>array</tref>
+ with a single value, the processor MAY represent this as a string value.
+ </p>
+ </section>
+
+ <section>
+ <h3>Initial Context</h3>
+ <p>The <tref>initial context</tref> is initialized as follows:</p>
+ <ul>
+ <li>
+ <code>@base</code> is set using <cite><href="http://www.ietf.org/rfc/rfc2396.txt">section 5.1 Establishing a
+ Base URI</href="http://www.ietf.org/rfc/rfc2396.txt"></cite> of [[RFC3986]]. Processors MAY provide a means
+ of setting the base IRI programatically.
+ </li>
+ <li><code>@coerce</code> is set with a single mapping from <code>@iri</code> to <code>@type</code>.</li>
+ </ul>
+ <pre class="example" data-transform="updateExample">
+ <!--
+ {
+ "@base": ****document-location****,
+ "@coerce": {
+ "@iri": "@type"
+ }
+ }
+ -->
+ </pre>
+ </section>
+</section>
+
+<section>
+ <h2>IRI Expansion</h2>
+ <p>Keys and some values are evaluated to produce an IRI. This section defines an algorithm for
+ transforming a value representing an IRI into an actual IRI.</p>
+ <p>IRIs may be represented as an absolute IRI, a <tref>term</tref>, a <tref>prefix</tref>:<tref>term</tref> construct, or as a value relative to <code>@base</code>
+ or <code>@vocab</code>.</p>
+ <p>The algorithm for generating an IRI is:
+ <ol class="algorithm">
+ <li>Split the value into a <em>prefix</em> and <em>suffix</em> from the first occurrence of ':'.</li>
+ <li>If the prefix is a '_' (underscore), the IRI is unchanged.</li>
+ <li>If the <tref>active context</tref> contains a mapping for <em>prefix</em>, generate an IRI
+ by prepending the mapped prefix to the (possibly empty) suffix using textual concatenation. Note that an empty
+ suffix and no suffix (meaning the value contains no ':' string at all) are treated equivalently.</li>
+ <li>If the IRI being processed is for a property (i.e., a key's value in a <tref>JSON object</tref>, or a
+ value in a <code>@coerce</code> mapping) and the active context has a <code>@vocab</code> mapping,
+ join the mapped value to the suffix using textual concatenation.</li>
+ <li>If the IRI being processed is for a subject or object (i.e., not a property) and the active context has a <code>@base</code> mapping,
+ join the mapped value to the suffix using the method described in [[!RFC3986]].</li>
+ <li>Otherwise, use the value directly as an IRI.</li>
+ </ol>
+ </p>
+</section>
+
+<section>
+ <h2>IRI Compaction</h2>
+ <p>Some keys and values are expressed using IRIs. This section defines an
+ algorithm for transforming an IRI to a compact IRI using the
+ <tref>term</tref>s and <tref>prefix</tref>es specified in the
+ <tref>local context</tref>.</p>
+
+ <p>The algorithm for generating a compacted IRI is:
+ <ol class="algorithm">
+ <li>Search every key-value pair in the <tref>active context</tref> for
+ a <tref>term</tref> that is a complete match
+ against the IRI. If a complete match is found, the resulting compacted
+ IRI is the <tref>term</tref> associated with the IRI in the
+ <tref>active context</tref>.</li>
+ <li>If a complete match is not found, search for a partial match from
+ the beginning of the IRI. For all matches that are found, the resulting
+ compacted IRI is the <tref>prefix</tref> associated with the partially
+ matched IRI in the <tref>active context</tref> concatenated with a
+ colon (:) character and the unmatched part of the string. If there is
+ more than one compacted IRI produced, the final value is the
+ shortest and lexicographically least value of the entire set of compacted IRIs.</li>
+ </ol>
+ </p>
+</section>
+
+<section>
+ <h2>Value Expansion</h2>
+ <p>Some values in JSON-LD can be expressed in a compact form. These values
+ are required to be expanded at times when processing JSON-LD documents.
+ </p>
+
+ <p>The algorithm for expanding a value is:
+ <ol class="algorithm">
+ <li>If the key that is associated with the value has an associated
+ coercion entry in the <tref>local context</tref>, the resulting
+ expansion is an object populated according to the following steps:
+ <ol class="algorithm">
+ <li>If the coercion target is <code>@iri</code>, expand the value
+ by adding a new key-value pair where the key is <code>@iri</code>
+ and the value is the expanded IRI according to the
+ <a href="#iri-expansion">IRI Expansion</a> rules.</li>
+ <li>If the coercion target is a typed literal, expand the value
+ by adding two new key-value pairs. The first key-value pair
+ will be <code>@literal</code> and the unexpanded value. The second
+ key-value pair will be <code>@datatype</code> and the associated
+ coercion datatype expanded according to the
+ <a href="#iri-expansion">IRI Expansion</a> rules.</li>
+ </ol>
+ </li>
+ </ol>
+ </p>
+</section>
+
+<section>
+ <h2>Value Compaction</h2>
+ <p>Some values, such as IRIs and typed literals, may be expressed in an
+ expanded form in JSON-LD. These values are required to be compacted at
+ times when processing JSON-LD documents.
+ </p>
+
+ <p>The algorithm for compacting a value is:
+ <ol class="algorithm">
+ <li>If the <tref>local context</tref> contains a coercion target for the
+ key that is associated with the value, compact the value using the
+ following steps:
+ <ol class="algorithm">
+ <li>If the coercion target is an <code>@iri</code>, the compacted
+ value is the value associated with the <code>@iri</code> key,
+ processed according to the
+ <a href="#iri-compaction">IRI Compaction</a> steps.</li>
+ <li>If the coercion target is a typed literal, the compacted
+ value is the value associated with the <code>@literal</code> key.
+ </li>
+ <li>Otherwise, the value is not modified.</li>
+ </ol>
+ </li>
+ </ol>
+ </p>
+</section>
+
+<section>
+<h2>Expansion</h2>
+
+<p class="issue">This algorithm is a work in progress, do not implement it.</p>
+
+<p>As stated previously, expansion is the process of taking a JSON-LD
+input and expanding all IRIs and typed literals to their fully-expanded form.
+The output will not contain a single context declaration and will have all IRIs
+and typed literals fully expanded.
+</p>
+
+<section>
+<h3>Expansion Algorithm</h3>
+
+<ol class="algorithm">
+ <li>If the top-level item in the <tref>JSON-LD input</tref> is an <tref>array</tref>,
+ process each item in the <tref>array</tref> recursively using this algorithm.</li>
+ <li>If the top-level item in the <tref>JSON-LD input</tref> is an object,
+ update the <tref>local context</tref> according to the steps outlined in
+ the <a href="#context">context</a> section. Process each key, expanding
+ the key according to the <a href="#iri-expansion">IRI Expansion</a> rules.</li>
+ <ol class="algorithm">
+ <li>Process each value associated with each key:
+ <ol class="algorithm">
+ <li>If the value is an <tref>array</tref>, process each item in the <tref>array</tref>
+ recursively using this algorithm.</li>
+ <li>If the value is an object, process the object recursively
+ using this algorithm.</li>
+ <li>Otherwise, check to see the associated key has an associated
+ coercion rule. If the value should be coerced, expand the value
+ according to the <a href="#value-expansion">Value Expansion</a> rules.
+ If the value does not need to be coerced, leave the value as-is.
+ </li>
+ </ol>
+ <li>Remove the context from the object.</li>
+ </ol>
+</ol>
+</section>
+
+</section>
+
+<section>
+<h2>Compaction</h2>
+
+<p class="issue">This algorithm is a work in progress, do not implement it.</p>
+
+<p>As stated previously, compaction is the process of taking a JSON-LD
+input and compacting all IRIs using a given context. The output
+will contain a single top-level context declaration and will only use
+<tref>term</tref>s and <tref>prefix</tref>es and will ensure that all
+typed literals are fully compacted.
+</p>
+
+<section>
+<h3>Compaction Algorithm</h3>
+
+<ol class="algorithm">
+ <li>Perform the <a href="#expansion-algorithm">Expansion Algorithm</a> on
+ the <tref>JSON-LD input</tref>. This removes any existing context to allow the given context to be cleanly applied.</li>
+ <li>Set the <tref>active context</tref> to the given context.
+ <li>If the top-level item is an <tref>array</tref>, process each item in the <tref>array</tref>
+ recursively, starting at this step.
+ <li>If the top-level item is an object, compress each key using the steps
+ defined in <a href="#iri-compaction">IRI Compaction</a> and compress each
+ value using the steps defined in
+ <a href="#value-compaction">Value Compaction</a>.</li>
+ </li>
+</ol>
+</section>
+
+</section>
+
+
+<section>
+<h2>Framing</h2>
+
+<p class="issue">This algorithm is a work in progress, do not implement it.</p>
+
+<p>A JSON-LD document is a representation of a directed graph. A single
+directed graph can have many different serializations, each expressing
+exactly the same information. Developers typically don't work directly with
+graphs, but rather, prefer trees when dealing with JSON. While mapping a graph
+to a tree can be done, the layout of the end result must be specified in
+advance. This section defines an algorithm for mapping a graph to
+a tree given a <tref>frame</tref>.
+</p>
+
+<section>
+<h3>Framing Algorithm Terms</h3>
+ <dl>
+ <dt><tdef>input frame</tdef></dt>
+ <dd>
+ the initial <tref>frame</tref> provided to the framing algorithm.
+ </dd>
+ <dt><tdef>framing context</tdef></dt>
+ <dd>
+ a context containing the <tref>object embed flag</tref>, the
+ <tref>explicit inclusion flag</tref> and the
+ <tref>omit default flag</tref>.
+ </dd>
+ <dt><tdef>object embed flag</tdef></dt>
+ <dd>
+ a flag specifying that objects should be directly embedded in the output,
+ instead of being referred to by their IRI.
+ </dd>
+ <dt><tdef>explicit inclusion flag</tdef></dt>
+ <dd>
+ a flag specifying that for properties to be included in the output, they
+ must be explicitly declared in the <tref>framing context</tref>.
+ </dd>
+ <dt><tdef>omit missing properties flag</tdef></dt>
+ <dd>
+ a flag specifying that properties that are missing from the
+ <tref>JSON-LD input</tref> should be omitted from the output.
+ </dd>
+ <dt><tdef>match limit</tdef></dt>
+ <dd>
+ A value specifying the maximum number of matches to accept when building
+ arrays of values during the framing algorithm. A value of -1 specifies
+ that there is no match limit.
+ </dd>
+ <dt><tdef>map of embedded subjects</tdef></dt>
+ <dd>
+ A map that tracks if a subject has been embedded in the output of the
+ <a href="#framing-algorithm">Framing Algorithm</a>.
+ </dd>
+ </dl>
+</section>
+
+<section>
+<h3>Framing Algorithm</h3>
+
+<p>The framing algorithm takes <tref>JSON-LD input</tref> that has been
+normalized according to the
+<a href="#normalization-algorithm">Normalization Algorithm</a>
+(<strong>normalized input</strong>), an
+<tref>input frame</tref> that has been expanded according to the
+<a href="#expansion-algorithm">Expansion Algorithm</a>
+(<strong>expanded frame</strong>), and a number of options and produces
+<tref>JSON-LD output</tref>. The following series of steps is the recursive
+portion of the framing algorithm:
+</p>
+
+<ol class="algorithm">
+ <li>Initialize the <tref>framing context</tref> by setting the
+ <tref>object embed flag</tref>, clearing the
+ <tref>explicit inclusion flag</tref>, and clearing the
+ <tref>omit missing properties flag</tref>. Override these values
+ based on input options provided to the algorithm by the application.
+ </li>
+ <li>Generate a <tdef>list of frames</tdef> by processing the
+ <strong>expanded frame</strong>:
+ <ol class="algorithm">
+ <li>If the <strong>expanded frame</strong> is not an <tref>array</tref>, set
+ <tref>match limit</tref> to 1, place the
+ <strong>expanded frame</strong> into the <tref>list of frames</tref>,
+ and set the <tref>JSON-LD output</tref> to <code>null</code>.</li>
+ <li>If the <strong>expanded frame</strong> is an empty <tref>array</tref>, place an
+ empty object into the <tref>list of frames</tref>,
+ set the <tref>JSON-LD output</tref> to an <tref>array</tref>, and set
+ <tref>match limit</tref> to -1.</li>
+ <li>If the <strong>expanded frame</strong> is a non-empty <tref>array</tref>, add
+ each item in the <strong>expanded frame</strong> into the
+ <tref>list of frames</tref>, set the <tref>JSON-LD output</tref> to an
+ <tref>array</tref>, and set <tref>match limit</tref> to -1.</li>
+ </ol></li>
+ <li>Create a <tdef>match array</tdef> for each <strong>expanded frame</strong>
+ in the <tref>list of frames</tref> halting when either the
+ <tref>match limit</tref> is zero or the end of the
+ <tref>list of frames</tref> is reached. If an
+ <strong>expanded frame</strong> is
+ not an object, the processor MUST throw a <code>Invalid Frame Format</code>
+ exception. Add each matching item from the <strong>normalized input</strong>
+ to the <tref>matches array</tref> and decrement the
+ <tref>match limit</tref> by 1 if:
+ <ol class="algorithm">
+ <li>The <strong>expanded frame</strong> has an <code>rdf:type</code>
+ that exists in the item's list of <code>rdf:type</code>s. Note:
+ the <code>rdf:type</code> can be an <tref>array</tref>, but only one value needs
+ to be in common between the item and the
+ <strong>expanded frame</strong> for a match.</li>
+ <li>The <strong>expanded frame</strong> does not have an
+ <code>rdf:type</code> property, but every property in the
+ <strong>expanded frame</strong> exists in the item.</li>
+ </ol></li>
+ <li>Process each item in the <tref>match array</tref> with its associated
+ <tdef>match frame</tdef>:
+ <ol class="algorithm">
+ <li>If the <tref>match frame</tref> contains an <code>@embed</code>
+ keyword, set the <tref>object embed flag</tref> to its value.
+ If the <tref>match frame</tref> contains an <code>@explicit</code>
+ keyword, set the <tref>explicit inclusion flag</tref> to its value.
+ Note: if the keyword exists, but the value is neither
+ <code>true</code> or <code>false</code>, set the associated flag to
+ <code>true</code>.</li>
+ <li>If the <tref>object embed flag</tref> is cleared and the item has
+ the <code>@subject</code> property, replace the item with the value
+ of the <code>@subject</code> property.</li>
+ <li>If the <tref>object embed flag</tref> is set and the item has
+ the <code>@subject</code> property, and its IRI is in the
+ <tref>map of embedded subjects</tref>, throw a
+ <code>Duplicate Embed</code> exception.</li>
+ <li>If the <tref>object embed flag</tref> is set and the item has
+ the <code>@subject</code> property and its IRI is not in the
+ <tref>map of embedded subjects</tref>:
+ <ol class="algorithm">
+ <li>If the <tref>explicit inclusion flag</tref> is set,
+ then delete any key from the item that does not exist in the
+ <tref>match frame</tref>, except <code>@subject</code>.</li>
+ <li>For each key in the <tref>match frame</tref>, except for
+ keywords and <code>rdf:type</code>:
+ <ol class="algorithm">
+ <li>If the key is in the item, then build a new
+ <tdef>recursion input list</tdef> using the object or objects
+ associated with the key. If any object contains an
+ <code>@iri</code> value that exists in the
+ <tref>normalized input</tref>, replace the object in the
+ <tref>recusion input list</tref> with a new object containing
+ the <code>@subject</code> key where the value is the value of
+ the <code>@iri</code>, and all of the other key-value pairs for
+ that subject. Set the <tdef>recursion match frame</tdef> to the
+ value associated with the <tref>match frame</tref>'s key. Replace
+ the value associated with the key by recursively calling this
+ algorithm using <tref>recursion input list</tref>,
+ <tref>recursion match frame</tref> as input.</li>
+ <li>If the key is not in the item, add the key to the item and
+ set the associated value to an empty array if the
+ <tref>match frame</tref> key's value is an array
+ or <code>null</code> otherwise.</li>
+ <li>If value associated with the item's key is <code>null</code>,
+ process the <tref>omit missing properties flag</tref>:
+ <ol class="algorithm">
+ <li>If the value associated with the key in the
+ <tref>match frame</tref> is an array, use the first frame
+ from the array as the <tdef>property frame</tdef>, otherwise
+ set the <tref>property frame</tref> to an empty object.</li>
+ <li>If the <tref>property frame</tref> contains an
+ <code>@omitDefault</code> keyword, set the
+ <tref>omit missing properties flag</tref> to its value.
+ Note: if the keyword exists, but the value is neither
+ <code>true</code> or <code>false</code>, set the associated
+ flag to <code>true</code>.</li>
+ <li>If the <tref>omit missing properties flag</tref> is set,
+ delete the key in the item. Otherwise, if the
+ <code>@default</code> keyword is set in the
+ <tref>property frame</tref> set the item's value to the value
+ of <code>@default</code>.</li>
+ </ol></li>
+ </ol></li>
+ </ol>
+ <li>If the <tref>JSON-LD output</tref> is <code>null</code> set it to
+ the item, otherwise, append the item to the
+ <tref>JSON-LD output</tref>.
+ </ol>
+ <li>Return the <tref>JSON-LD output</tref>.</li>
+</ol>
+
+The final, non-recursive step of the framing algorithm requires the
+<tref>JSON-LD output</tref> to be compacted according to the
+<a href="#compaction-algorithm">Compaction Algorithm</a> by using the
+context provided in the <tref>input frame</tref>. The resulting value is the
+final output of the compaction algorithm and is what should be returned to the
+application.
+
+</section>
+
+</section>
+
+<section>
+<h2>Normalization</h2>
+
+<p class="issue">This algorithm is a work in progress, do not implement it.</p>
+
+<p>Normalization is the process of taking <tref>JSON-LD input</tref> and
+performing a deterministic transformation on that input that results in all
+aspects of the graph being fully expanded and named in the
+<tref>JSON-LD output</tref>. The normalized output is generated in such a way
+that any conforming JSON-LD processor will generate identical output
+given the same input. The problem is a fairly difficult technical
+problem to solve because it requires a directed graph to be ordered into a
+set of nodes and edges in a deterministic way. This is easy to do when all of
+the nodes have unique names, but very difficult to do when some of the nodes
+are not labeled.
+</p>
+
+<p>In time, there may be more than one normalization algorithm that will need
+to be identified. For identification purposes, this algorithm is named
+"Universal Graph Normalization Algorithm 2011"
+(<abbr title="Universal Graph Normalization Algorithm 2011">UGNA2011</abbr>).
+</p>
+
+<section>
+<h3>Normalization Algorithm Terms</h3>
+ <dl>
+ <dt><tdef>label</tdef></dt>
+ <dd>
+ The subject IRI associated with a graph node. The subject IRI is expressed
+ using a key-value pair in a <tref>JSON object</tref> where the key is
+ <code>@subject</code> and the value is a string that is an IRI or
+ a <tref>JSON object</tref> containing the key <code>@iri</code> and
+ a value that is a string that is an IRI.
+ </dd>
+ <dt><tdef>list of expanded nodes</tdef></dt>
+ <dd>
+ A list of all nodes in the <tref>JSON-LD input</tref> graph containing no
+ embedded objects and having all keys and values expanded according to the
+ steps in the <a href="#expansion-algorithm">Expansion Algorithm</a>.
+ </dd>
+ <dt><tdef>alpha</tdef> and <tdef>beta</tdef> values</dt>
+ <dd>
+ The words <tref>alpha</tref> and <tref>beta</tref> refer to the first and
+ second nodes or values being examined in an algorithm. The names are
+ merely used to refer to each input value to a comparison algorithm.
+ </dd>
+ <dt><tdef>renaming counter</tdef></dt>
+ <dd>
+ A counter that is used during the
+ <a href="#node-relabeling-algorithm">Node Relabeling Algorithm</a>. The
+ counter typically starts at one (1) and counts up for every node that is
+ relabeled. There will be two such renaming counters in an implementation
+ of the normalization algorithm. The first is the
+ <tref>labeling counter</tref> and the second is the
+ <tref>deterministic labeling counter</tref>.
+ </dd>
+ <dt><tdef>serialization label</tdef></dt>
+ <dd>
+ An identifier that is created to aid in the normalization process in the
+ <a href="#deep-comparison-algorithm">Deep Comparison Algorithm</a>. The
+ value typically takes the form of <code>s<NUMBER></code> or
+ <code>c<NUMBER></code>.
+ </dd>
+</dl>
+</section>
+
+<section>
+<h3>Normalization State</h3>
+
+<p>When performing the steps required by the normalization algorithm,
+it is helpful to track the many pieces of information in a
+data structure called the <tdef>normalization state</tdef>. Many of these
+pieces simply provide indexes into the graph. The information
+contained in the <tref>normalization state</tref> is described below.</p>
+
+<dl>
+ <dt><tdef>node state</tdef></dt>
+ <dd>
+ Each node in the graph will be assigned a <tref>node state</tref>. This
+ state contains the information necessary to deterministically
+ <tref>label</tref> all nodes in the graph. A <tref>node state</tref>
+ includes:
+ <dl>
+ <dt><tdef>node reference</tdef></dt>
+ <dd>
+ A <tref>node reference</tref> is a reference to a node in the graph.
+ For a given <tref>node state</tref>, its <tref>node reference</tref>
+ refers to the node that the state is for. When a
+ <tref>node state</tref> is created, its <tref>node reference</tref>
+ should be to the node it is created for.
+ </dd>
+ <dt><tdef>outgoing list</tdef></dt>
+ <dd>
+ Lists the <tref>label</tref>s for all nodes that are properties of
+ the <tref>node reference</tref>. This list should be initialized
+ by iterating over every object associated with a property in the
+ <tref>node reference</tref> adding its label if it is another node.
+ </dd>
+ <dt><tdef>incoming list</tdef></dt>
+ <dd>
+ Lists the <tref>label</tref>s for all nodes in the graph for which
+ the <tref>node reference</tref> is a property. This list is
+ initialized to an empty list.
+ </dd>
+ <dt><tdef>outgoing serialization map</tdef></dt>
+ <dd>
+ Maps node <tref>label</tref>s to <tref>serialization label</tref>s.
+ This map is initialized to an empty map. When this map is populated,
+ it will be filled with keys that are the <tref>label</tref>s of every node in the
+ graph with a label that begins with <code>_:</code> and that has a
+ path, via properties, that starts with the
+ <tref>node reference</tref>.
+ </dd>
+ <dt><tdef>outgoing serialization</tdef></dt>
+ <dd>
+ A string that can be lexicographically compared to the
+ <tref>outgoing serialization</tref>s of other
+ <tref>node state</tref>s. It is a representation of the
+ <tref>outgoing serialization map</tref> and other related
+ information. This string is initialized to an empty string.
+ </dd>
+ <dt><tdef>incoming serialization map</tdef></dt>
+ <dd>
+ Maps node <tref>label</tref>s to <tref>serialization label</tref>s.
+ This map is initialized to an empty map. When this map is populated,
+ it will be filled with keys that are the <tref>label</tref>s of every
+ node in the graph with a <tref>label</tref> that begins with
+ <code>_:</code> and that has a path, via properties, that ends with
+ the <tref>node reference</tref>.
+ </dd>
+ <dt><tdef>incoming serialization</tdef></dt>
+ <dd>
+ A string that can be lexicographically compared to the
+ <tref>outgoing serialization</tref>s of other
+ <tref>node state</tref>s. It is a representation of the
+ <tref>incoming serialization map</tref> and other related
+ information. This string is initialized to an empty string.
+ </dd>
+ </dl>
+ </dd>
+ <dt><tdef>node state map</tdef></dt>
+ <dd>
+ A mapping from a node's <tref>label</tref> to a <tref>node state</tref>.
+ It is initialized to an empty map.
+ </dd>
+ <dt><tdef>labeling prefix</tdef></dt>
+ <dd>
+ The labeling prefix is a string that is used as the beginning of a node
+ <tref>label</tref>. It should be initialized to a random base string that
+ starts with the characters <code>_:</code>, is not used by any other
+ node's <tref>label</tref> in the <tref>JSON-LD input</tref>, and does not
+ start with the characters <code>_:c14n</code>. The prefix has two uses.
+ First it is used to temporarily name nodes during the normalization
+ algorithm in a way that doesn't collide with the names that already
+ exist as well as the names that will be generated by the normalization
+ algorithm. Second, it will eventually be set to <code>_:c14n</code> to
+ generate the final, deterministic labels for nodes in the graph. This
+ prefix will be concatenated with the <tref>labeling counter</tref> to
+ produce a node <tref>label</tref>. For example, <code>_:j8r3k</code> is
+ a proper initial value for the <tref>labeling prefix</tref>.
+ </dd>
+ <dt><tdef>labeling counter</tdef></dt>
+ <dd>
+ A counter that is used to label nodes. It is appended to the
+ <tref>labeling prefix</tref> to create a node <tref>label</tref>. It is
+ initialized to <code>1</code>.
+ </dd>
+ <dt><tdef>map of flattened nodes</tdef></dt>
+ <dd>
+ A map containing a representation of all nodes in the graph where the
+ key is a node <tref>label</tref> and the value is a single
+ <tref>JSON object</tref> that has no nested sub-objects
+ and has had all properties for the same node merged into a single
+ <tref>JSON object</tref>.
+ </dd>
+</dl>
+
+</section>
+
+<section>
+<h3>Normalization Algorithm</h3>
+
+<p>The normalization algorithm expands the <tref>JSON-LD input</tref>,
+flattens the data structure, and creates an initial set of names for all
+nodes in the graph. The flattened data structure is then processed by a
+node labeling algorithm in order to get a fully expanded and named list of
+nodes which is then sorted. The result is a deterministically named and
+ordered list of graph nodes.
+</p>
+
+<ol class="algorithm">
+<li>Expand the <tref>JSON-LD input</tref> according to the steps in
+the <a href="#expansion-algorithm">Expansion Algorithm</a> and store the
+result as the <strong>expanded input</strong>.</li>
+<li>Create a <tref>normalization state</tref>.</li>
+<li>Initialize the <tref>map of flattened nodes</tref> by recursively
+processing every <tdef>expanded node</tdef> in the
+<strong>expanded input</strong> in depth-first order:
+ <ol class="algorithm">
+ <li>If the <tref>expanded node</tref> is an unlabeled node, add a
+ new key-value pair to the <tref>expanded node</tref>
+ where the key is <code>@subject</code> and the value is the
+ concatenation of the <tref>labeling prefix</tref>
+ and the string value of the <tref>labeling counter</tref>.
+ Increment the <tref>labeling counter</tref>.</li>
+ <li>Add the <tref>expanded node</tref> to the
+ <tref>map of flattened nodes</tref>:
+ <ol class="algorithm">
+ <li>If the <tref>expanded node</tref>'s <tref>label</tref> is already
+ in the
+ <tref>map of flattened nodes</tref> merge all properties from the
+ entry in the <tref>map of flattened nodes</tref> into the
+ <tref>expanded node</tref>.</li>
+ <li>Go through every property associated with an array in the
+ <tref>expanded node</tref> and remove any duplicate IRI entries from
+ the array. If the resulting array only has one IRI entry, change it
+ from an array to an object.</li>
+ <li>Set the entry for the <tref>expanded node</tref>'s <tref>label</tref>
+ in the <tref>map of flattened nodes</tref> to the
+ <tref>expanded node</tref>.
+ </li></ol></li>
+ <li>After exiting the recursive step, replace the reference to the
+ <tref>expanded node</tref> with an object containing a single
+ key-value pair where the key is <code>@iri</code> and the value is
+ the value of the <code>@subject</code> key in the node.</li>
+ </ol></li>
+<li>For every entry in the <tref>map of flattened nodes</tref>, insert a
+ key-value pair into the <tref>node state map</tref> where the key is the
+ key from the <tref>map of flattened nodes</tref> and the value is a
+ <tref>node state</tref> where its <tref>node reference</tref> refers to
+ the value from the <tref>map of flattened nodes</tref>.
+<li>Populate the <tref>incoming list</tref> for each <tref>node state</tref>
+ by iterating over every node in the graph and adding its <tref>label</tref>
+ to the <tref>incoming list</tref> associated with each node found in its
+ properties.</li>
+<li>For every entry in the <tref>node state map</tref> that has a
+<tref>label</tref> that begins with <code>_:c14n</code>, relabel the node
+using the <a href="#node-relabeling-algorithm">Node Relabeling Algorithm</a>.
+<li>Label all of the nodes that contain a <code>@subject</code> key associated
+with a value starting with <code>_:</code> according to the steps in the
+<a href="#deterministic-labeling-algorithm">Deterministic Labeling Algorithm</a>.
+</li>
+</ol>
+</section>
+
+<section>
+<h4>Node Relabeling Algorithm</h4>
+
+<p>This algorithm renames a node by generating a unique
+<tdef>new label</tdef> and updating all references to that <tref>label</tref>
+in the <tref>node state map</tref>. The <tdef>old label</tdef> and the
+<tref>normalization state</tref> must be given as an input to the
+algorithm. The <tref>old label</tref> is the current <tref>label</tref> of
+the node that is to be relabeled.
+
+<p>The node relabeling algorithm is as follows:</p>
+
+<ol class="algorithm">
+ <li>If the <tref>labeling prefix</tref> is <code>_:c14n</code> and the
+ <tref>old label</tref> begins with <code>_:c14n</code> then return as
+ the node has already been renamed.
+ </li>
+ <li>Generate the <tdef>new label</tdef> by concatenating the
+ <tref>labeling prefix</tref> with the string value of the
+ <tref>labeling counter</tref>. Increment the <tref>labeling counter</tref>.
+ </li>
+ <li>For the <tref>node state</tref> associated with the
+ <tref>old label</tref>, update every node in the <tref>incoming list</tref>
+ by changing all the properties that reference the <tref>old label</tref> to
+ the <tref>new label</tref>.
+ </li>
+ <li>Change the <tref>old label</tref> key in the <tref>node state map</tref>
+ to the <tref>new label</tref> and set the associated
+ <tref>node reference</tref>'s <tref>label</tref> to the
+ <tref>new label</tref>.
+ </li>
+</ol>
+</section>
+
+<section>
+<h4>Deterministic Labeling Algorithm</h4>
+
+<p>The deterministic labeling algorithm takes the
+<tref>normalization state</tref>
+and produces a <tdef>list of finished nodes</tdef> that is sorted and
+contains deterministically named and expanded nodes from the graph.
+
+<ol class="algorithm">
+ <li>Set the <tref>labeling prefix</tref> to <code>_:c14n</code>, the
+ <tref>labeling counter</tref> to <code>1</code>,
+ the <tdef>list of finished nodes</tdef> to an empty array, and create
+ an empty array, the <tdef>list of unfinished nodes</tdef>.</li>
+ <li>For each <tref>node reference</tref> in the <tref>node state map</tref>:
+ <ol class="algorithm">
+ <li>If the node's <tref>label</tref> does not start with <code>_:</code>
+ then put the <tref>node reference</tref> in the
+ <tref>list of finished nodes</tref>.
+ </li>
+ <li>If the node's <tref>label</tref> does start with <code>_:</code>
+ then put the <tref>node reference</tref> in the
+ <tref>list of unfinished nodes</tref>.
+ </li>
+ </ol>
+ </li>
+ <li>Append to the <tref>list of finished nodes</tref> by processing
+ the remainder of the <tref>list of unfinished nodes</tref> until it is
+ empty:
+ <ol class="algorithm">
+ <li>Sort the <tref>list of unfinished nodes</tref> in descending order
+ according to the
+ <a href="#deep-comparison-algorithm">Deep Comparison Algorithm</a> to
+ determine the sort order.</li>
+ <li>Create a <tdef>list of labels</tdef> and initialize it to an
+ empty array.</li>
+ <li>For the first node from the <tref>list of unfinished nodes</tref>:
+ <ol class="algorithm">
+ <li>Add its <tref>label</tref> to the <tref>list of labels</tref>.
+ </li>
+ <li>For each key-value pair from its associated
+ <tref>outgoing serialization map</tref>, add the key to a list and
+ then sort the list according to the lexicographical order of the
+ keys' associated values. Append the list to the
+ <tref>list of nodes to label</tref>.
+ </li>
+ <li>For each key-value pair from its associated
+ <tref>incoming serialization map</tref>, add the key to a list and
+ then sort the list according to the lexicographical order of the
+ keys' associated values. Append the list to the
+ <tref>list of nodes to label</tref>.
+ </li></ol></li>
+ <li>For each <tref>label</tref> in the <tref>list of labels</tref>,
+ relabel the associated node according to the
+ <a href="#node-relabeling-algorithm">Node Relabeling Algorithm</a>. If
+ any <tref>outgoing serialization map</tref> contains a key that
+ matches the <tref>label</tref>, clear the map and set the associated
+ <tref>outgoing serialization</tref> to an empty string. If any
+ <tref>incoming serialization map</tref> contains a key that
+ matches the <tref>label</tref>, clear the map and set the associated
+ <tref>incoming serialization</tref> to an empty string.
+ </li>
+ <li>
+ Remove each node with a <tref>label</tref> that starts with
+ <code>_:c14n</code> from the <tref>list of unfinished nodes</tref> and
+ add it to the <tref>list of finished nodes</tref>.
+ </li>
+ </ol>
+ </li>
+ <li>Sort the <tref>list of finished nodes</tref> in descending order
+ according to the
+ <a href="#deep-comparison-algorithm">Deep Comparison Algorithm</a> to
+ determine the sort order.</li>
+</ol>
+</section>
+
+<section>
+<h4>Shallow Comparison Algorithm</h4>
+
+<p>
+The shallow comparison algorithm takes two unlabeled nodes,
+<tref>alpha</tref> and <tref>beta</tref>, as input and
+determines which one should come first in a sorted list. The following
+algorithm determines the steps that are executed in order to determine the
+node that should come first in a list:
+</p>
+
+<ol class="algorithm">
+ <li>Compare the total number of node properties. The node with fewer
+ properties is first.</li>
+ <li>Lexicographically sort the property IRIs for each node and compare
+ the sorted lists. If an IRI is found to be lexicographically smaller, the
+ node containing that IRI is first.</li>
+ <li>Compare the values of each property against one another:
+ <ol class="algorithm">
+ <li>The node associated with fewer property values is first.
+ </li>
+ <li>Create an <tdef>alpha list</tdef> by adding all values associated
+ with the <tref>alpha</tref> property that are not unlabeled nodes.
+ </li>
+ <li>Create a <tdef>beta list</tdef> by adding all values associated
+ with the <tref>beta</tref> property that is not an unlabeled node.
+ </li>
+ <li>Compare the length of <tref>alpha list</tref> and
+ <tref>beta list</tref>. The node associated with the list containing
+ the fewer number of items is first.</li>
+ <li>Sort <tref>alpha list</tref> and <tref>beta list</tref> according to
+ the
+ <a href="#object-comparison-algorithm">Object Comparison Algorithm</a>.
+ For each offset into the <tref>alpha list</tref>, compare the item
+ at the offset against the item at the same offset in the
+ <tref>beta list</tref> according to the
+ <a href="#object-comparison-algorithm">Object Comparison Algorithm</a>.
+ The node associated with the lesser item is first.
+ </ol></li>
+ <li>Process the <tref>incoming list</tref>s associated with each node to
+ determine order:
+ <ol class="algorithm">
+ <li>The node with the shortest <tref>incoming list</tref> is first.</li>
+ <li>Sort the <tref>incoming list</tref>s according to incoming property
+ and then incoming <tref>label</tref>.
+ <li>The node associated with the fewest number of incoming nodes is
+ first.</li>
+ <li>For each offset into the <tref>incoming list</tref>s,
+ compare the associated properties and <tref>label</tref>s:
+ <ol class="algorithm">
+ <li>The node associated with a <tref>label</tref> that does not begin with
+ <code>_:</code> is first.
+ </li>
+ <li>If the nodes' <tref>label</tref>s do not begin with
+ <code>_:</code>, then the node associated with the
+ lexicographically lesser <tref>label</tref> is first.</li>
+ </li>
+ <li>The node associated with the lexicographically lesser associated
+ property is first.
+ </li>
+ <li>The node with the <tref>label</tref> that does not begin with
+ <code>_:c14n</code> is first.
+ </li>
+ <li>The node with the lexicographically lesser <tref>label</tref>
+ is first.
+ </li>
+ </ol>
+ </ol></li>
+ <li>Otherwise, the nodes are equivalent.</li>
+</section>
+
+<section>
+<h4>Object Comparison Algorithm</h4>
+
+<p>
+The object comparison algorithm is designed to compare two graph node
+property values, <tref>alpha</tref> and <tref>beta</tref>, against the other.
+The algorithm is useful when sorting two lists of graph node properties.
+</p>
+
+<ol class="algorithm">
+ <li>If one of the values is a <tref>string</tref> and the other is not, the value that is
+ a string is first.
+ </li>
+ <li>If both values are <tref>string</tref>s, the lexicographically lesser string is
+ first.
+ </li>
+ <li>If one of the values is a literal and the other is not, the value that is
+ a literal is first.
+ </li>
+ <li>If both values are literals:
+ <ol class="algorithm">
+ <li>The lexicographically lesser string associated with
+ <code>@literal</code> is first.
+ </li>
+ <li>The lexicographically lesser string associated with
+ <code>@datatype</code> is first.
+ </li>
+ <li>The lexicographically lesser string associated with
+ <code>@language</code> is first.
+ </li>
+ </ol>
+ </li>
+ <li>If both values are expanded IRIs, the
+ lexicographically lesser string associated with <code>@iri</code>
+ is first.</li>
+ <li>Otherwise, the two values are equivalent.</li>
+</ol>
+
+</section>
+
+<section>
+<h4>Deep Comparison Algorithm</h4>
+
+<p>
+The deep comparison algorithm is used to compare the difference between two
+nodes, <tref>alpha</tref> and <tref>beta</tref>.
+A deep comparison takes the incoming and outgoing node edges in
+a graph into account if the number of properties and value of those properties
+are identical. The algorithm is helpful when sorting a list of nodes and will
+return whichever node should be placed first in a list if the two nodes are
+not truly equivalent.
+</p>
+
+<p>When performing the steps required by the deep comparison algorithm, it
+is helpful to track state information about mappings. The information
+contained in a <tref>mapping state</tref> is described below.</p>
+
+<dl class="algorithm">
+ <dt><tdef>mapping state</tdef></dt>
+ <dd>
+ <dl>
+ <dt><tdef>mapping counter</tdef></dt>
+ <dd>
+ Keeps track of the number of nodes that have been mapped to
+ <tref>serialization labels</tref>. It is initialized to
+ <code>1</code>.
+ </dd>
+ <dt><tdef>processed labels map</tdef></dt>
+ <dd>
+ Keeps track of the <tref>label</tref>s of nodes that have already
+ been assigned <tref>serialization label</tref>s. It is initialized
+ to an empty map.
+ </dd>
+ <dt><tdef>serialized labels map</tdef></dt>
+ <dd>
+ Maps a node <tref>label</tref> to its associated
+ <tref>serialization label</tref>. It is initialized to an empty map.
+ </dd>
+ <dt><tdef>adjacent info map</tdef></dt>
+ <dd>
+ Maps a <tref>serialization label</tref> to the node
+ <tref>label</tref> associated with it, the list of sorted
+ <tref>serialization label</tref>s for adjacent nodes, and the map of
+ adjacent node <tref>serialiation label</tref>s to their associated
+ node <tref>label</tref>s. It is initialized to an empty map.
+ </dd>
+ <dt><tdef>key stack</tdef></dt>
+ <dd>
+ A stack where each element contains an array of adjacent
+ <tref>serialization label</tref>s and an index into that array. It
+ is initialized to a stack containing a single element where its
+ array contains a single string element <code>s1</code> and its
+ index is set to <code>0</code>.
+ </dd>
+ <dt><tdef>serialized keys</tdef></dt>
+ <dd>
+ Keeps track of which <tref>serialization label</tref>s have already
+ been written at least once to the <tref>serialization string</tref>.
+ It is initialized to an empty map.
+ </dd>
+ <dt><tdef>serialization string</tdef></dt>
+ <dd>
+ A string that is incrementally updated as a serialization is built.
+ It is initialized to an empty string.
+ </dd>
+ </dl>
+ </dd>
+</dl>
+
+<p>The deep comparison algorithm is as follows:</p>
+
+<ol class="algorithm">
+ <li>Perform a comparison between <tref>alpha</tref> and <tref>beta</tref>
+ according to the
+ <a href="#shallow-comparison-algorithm">Shallow Comparison Algorithm</a>.
+ If the result does not show that the two nodes are equivalent, return
+ the result.
+ </li>
+ <li>Compare incoming and outgoing edges for each node, updating their
+ associated <tref>node state</tref> as each node is processed:
+ <ol class="algorithm">
+ <li>If the <tref>outgoing serialization map</tref> for <tref>alpha</tref>
+ is empty, generate the serialization according to the
+ <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
+ Provide <tref>alpha</tref>'s <tref>node state</tref>, a new
+ <tref>mapping state</tref>,
+ <code>outgoing direction</code> to the algorithm as inputs.
+ <li>If the <tref>outgoing serialization map</tref> for <tref>beta</tref>
+ is empty, generate the serialization according to the
+ <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
+ Provide <tref>beta</tref>'s <tref>node state</tref>, a new
+ <tref>mapping state</tref>, and
+ <code>outgoing direction</code> to the algorithm as inputs.
+ <li>If <tref>alpha</tref>'s <tref>outgoing serialization</tref> is
+ lexicographically less than <tref>beta</tref>'s, then
+ <tref>alpha</tref> is first. If it is greater, then <tref>beta</tref>
+ is first.</li>
+ <li>If the <tref>incoming serialization map</tref> for <tref>alpha</tref>
+ is empty, generate the serialization according to the
+ <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
+ Provide <tref>alpha</tref>'s <tref>node state</tref>, a new
+ <tref>mapping state</tref> with its <tref>serialized labels map</tref>
+ set to a copy of <tref>alpha</tref>'s
+ <tref>outgoing serialization map</tref>, and
+ <code>incoming direction</code> to the algorithm as inputs.
+ <li>If the <tref>incoming serialization map</tref> for <tref>beta</tref>
+ is empty, generate the serialization according to the
+ <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
+ Provide <tref>beta</tref>'s <tref>node state</tref>, a new
+ <tref>mapping state</tref> with its <tref>serialized labels map</tref>
+ set to a copy of <tref>beta</tref>'s
+ <tref>outgoing serialization map</tref>, and
+ <code>incoming direction</code> to the algorithm as inputs.
+ <li>If <tref>alpha</tref>'s <tref>incoming serialization</tref> is
+ lexicographically less than <tref>beta</tref>'s, then
+ <tref>alpha</tref> is first. If it is greater, then <tref>beta</tref>
+ is first.</li>
+ </ol></li>
+</ol>
+</section>
+
+<section>
+<h4>Node Serialization Algorithm</h4>
+
+<p>
+The node serialization algorithm takes a <tref>node state</tref>, a
+<tref>mapping state</tref>, and a <tdef>direction</tdef> (either
+<code>outgoing direction</code> or <code>incoming direction</code>) as
+inputs and generates a deterministic serialization for the
+<tref>node reference</tref>.
+</p>
+
+<ol class="algorithm">
+<li>If the <tref>label</tref> exists in the
+ <tref>processed labels map</tref>, terminate the algorithm as the
+ <tref>serialization label</tref> has already been created.
+</li>
+<li>Set the value associated with the <tref>label</tref> in the
+ <tref>processed labels map</tref> to <code>true</code>.
+</li>
+<li>Generate the next <tdef>serialization label</tdef> for the
+ <tref>label</tref> according to the
+ <a href="#serialization-label-generation-algorithm">Serialization Label Generation Algorithm</a>.
+</li>
+<li>Create an empty map called the <tdef>adjacent serialized labels map</tdef>
+that will store mappings from <tref>serialized label</tref>s to adjacent
+node <tref>label</tref>s.</li>
+<li>Create an empty array called the
+<tdef>adjacent unserialized labels list</tdef> that will store
+<tref>label</tref>s of adjacent nodes that haven't been assigned
+<tref>serialization label</tref>s yet.
+</li>
+<li>For every <tref>label</tref> in a list, where the list the <tref>outgoing list</tref> if
+the <tref>direction</tref> is <code>outgoing direction</code> and the
+<tref>incoming list</tref> otherwise, if the <tref>label</tref> starts with
+<code>_:</code>, it is the <tdef>target node label</tdef>:
+ <ol class="algorithm">
+ <li>Look up the <tref>target node label</tref> in the
+ <tref>processed labels map</tref> and if a mapping exists,
+ update the <tref>adjacent serialized labels map</tref> where the key is
+ the value in the <tref>serialization map</tref> and the value is the
+ <tref>target node label</tref>.</li>
+ <li>Otherwise, add the <tref>target node label</tref> to the
+ <tref>adjacent unserialized labels list</tref>.
+ </ol>
+</li>
+<li>Set the <tdef>maximum serialization combinations</tdef> to
+ <code>1</code> or the length of the
+ <tref>adjacent unserialized labels list</tref>, whichever is greater.</li>
+<li>While the <tref>maximum serialization combinations</tref> is greater than
+ <code>0</code>, perform the
+ <a href="#combinatorial-serialization-algorithm">Combinatorial Serialization Algorithm</a>
+ passing the <tref>node state</tref>, the <tref>mapping state</tref> for the
+ first iteration and a copy of it for each subsequent iteration, the
+ generated <tref>serialization label</tref>, the <tref>direction</tref>,
+ the <tref>adjacent serialized labels map</tref>, and the
+ <tref>adjacent unserialized labels list</tref>.
+ Decrement the <tref>maximum serialization combinations</tref> by
+ <code>1</code> for each iteration.
+</ol>
+
+</section>
+
+<section>
+<h4>Serialization Label Generation Algorithm</h4>
+
+<p>
+The algorithm generates a <tref>serialization label</tref> given a
+<tref>label</tref> and a <tref>mapping state</tref> and returns the
+<tref>serialization label</tref>.
+</p>
+
+ <ol class="algorithm">
+ <li>If the <tref>label</tref> is already in the
+ <tref>serialization labels map</tref>, return its associated value.
+ </li>
+ <li>If the <tref>label</tref> starts with the string <code>_:c14n</code>,
+ the <tref>serialization label</tref> is the letter <code>c</code>
+ followed by the number that follows <code>_:c14n</code> in the
+ <tref>label</tref>.
+ </li>
+ <li>Otherwise, the <tref>serialization label</tref> is the
+ letter <code>s</code> followed by the string value of
+ <tref>mapping count</tref>. Increment the <tref>mapping count</tref> by
+ <code>1</code>.
+ </li>
+ <li>Create a new key-value pair in the <tref>serialization labels map</tref>
+ where the key is the <tref>label</tref> and the value is the
+ generated <tref>serialization label</tref>.
+ </li>
+ </ol>
+</section>
+
+<section>
+<h4>Combinatorial Serialization Algorithm</h4>
+
+<p>
+The combinatorial serialization algorithm takes a <tref>node state</tref>, a
+<tref>mapping state</tref>, a <tref>serialization label</tref>, a
+<tref>direction</tref>, a <tref>adjacent serialized labels map</tref>,
+and a <tref>adjacent unserialized labels list</tref> as inputs and generates
+the lexicographically least serialization of nodes relating to the
+<tref>node reference</tref>.
+</p>
+
+<ol class="algorithm">
+ <li>If the <tref>adjacent unserialized labels list</tref> is not empty:
+ <ol class="algorithm">
+ <li>Copy the <tref>adjacent serialized labels map</tref> to the
+ <tdef>adjacent serialized labels map copy</tdef>.</li>
+ <li>Remove the first <tref>unserialized label</tref> from the
+ <tref>adjacent unserialized labels list</tref> and create a new
+ <tdef>new serialization label</tdef> according to the
+ <a href="#serialization-label-generation-algorithm">Serialization Label Generation Algorithm</a>.
+ <li>Create a new key-value mapping in the
+ <tref>adjacent serialized labels map copy</tref>
+ where the key is the <tref>new serialization label</tref> and the value
+ is the <tref>unserialized label</tref>.
+ <li>Set the <tdef>maximum serialization rotations</tdef> to
+ <code>1</code> or the length of the
+ <tref>adjacent unserialized labels list</tref>, whichever is greater.
+ </li>
+ <li>While the <tref>maximum serialization rotations</tref> is greater than
+ <code>0</code>:
+ <ol class="algorithm">
+ <li>Recursively perform the
+ <a href="#combinatorial-serialization-algorithm">Combinatorial Serialization Algorithm</a>
+ passing the <tref>mapping state</tref> for the first iteration of the
+ loop, and a copy of it for each subsequent iteration.
+ </li>
+ <li>Rotate the elements in the
+ <tref>adjacent unserialized labels list</tref> by shifting each of
+ them once to the right, moving the element at the end of the list
+ to the beginning of the list.
+ </li>
+ <li>Decrement the <tref>maximum serialization rotations</tref> by
+ <code>1</code> for each iteration.
+ </li>
+ </ol>
+ </li>
+ </ol>
+ </li>
+ <li>If the <tref>adjacent unserialized labels list</tref> is empty:
+ <ol class="algorithm">
+ <li>Create a <tdef>list of keys</tdef> from the keys in the
+ <tref>adjacent serialized labels map</tref> and sort it
+ lexicographically.
+ </li>
+ <li>Add a key-value pair to the <tref>adjacent info map</tref> where
+ the key is the <tref>serialization label</tref> and the value is
+ an object containing the <tref>node reference</tref>'s label, the
+ <tref>list of keys</tref> and the
+ <tref>adjacent serialized labels map</tref>.
+ </li>
+ <li>Update the <tref>serialization string</tref> according to the
+ <a href="#mapping-serialization-algorithm">Mapping Serialization Algorithm</a>.
+ </li>
+ <li>If the <tref>direction</tref> is <code>outgoing direction</code>
+ then <tdef>directed serialization</tdef> refers to the
+ <tref>outgoing serialization</tref> and the
+ <tdef>directed serialization map</tdef> refers to the
+ <tref>outgoing serialization map</tref>, otherwise it refers to the
+ <tref>incoming serialization</tref> and the
+ <tref>directed serialization map</tref> refers to the
+ <tref>incoming serialization map</tref>. Compare the
+ <tref>serialization string</tref> to the
+ <tref>directed serialization</tref> according to the
+ <a href="#mapping-serialization-algorithm">Serialization Comparison Algorithm</a>.
+ If the <tref>serialization string</tref> is less than or equal to
+ the <tref>directed serialization</tref>:
+ <ol class="algorithm">
+ <li>For each value in the <tref>list of keys</tref>, run the
+ <a href="#node-serialization-algorithm">Node Serialization Algorithm</a>.
+ </li>
+ <li>Update the <tref>serialization string</tref> according to the
+ <a href="#mapping-serialization-algorithm">Mapping Serialization Algorithm</a>.
+ </li>
+ <li>Compare the <tref>serialization string</tref> to the
+ <tref>directed serialization</tref> again and if it is less than
+ or equal and the length of the <tref>serialization string</tref> is
+ greater than or equal to the length of the
+ <tref>directed serialization</tref>, then set the
+ <tref>directed serialization</tref> to the
+ <tref>serialization string</tref> and set the
+ <tref>directed serialization map</tref> to the
+ <tref>serialized labels map</tref>.
+ </li>
+ </ol>
+ </li>
+ </ol>
+ </li>
+</ol>
+
+</section>
+
+<section>
+<h4>Serialization Comparison Algorithm</h4>
+
+<p>
+The serialization comparison algorithm takes two serializations,
+<tref>alpha</tref> and <tref>beta</tref> and returns either which of the two
+is less than the other or that they are equal.
+</p>
+
+<ol class="algorithm">
+ <li>Whichever serialization is an empty string is greater. If they are
+ both empty strings, they are equal.</li>
+ <li>Return the result of a lexicographical comparison of <tref>alpha</tref>
+ and <tref>beta</tref> up to the number of characters in the shortest of
+ the two serializations.
+ </li>
+</ol>
+</section>
+
+<section>
+<h4>Mapping Serialization Algorithm</h4>
+
+<p>
+The mapping serialization algorithm incrementally updates the
+<tref>serialization string</tref> in a <tref>mapping state</tref>.
+</p>
+
+<ol class="algorithm">
+ <li>If the <tref>key stack</tref> is not empty:
+ <ol class="algorithm">
+ <li>Pop the <tdef>serialization key info</tdef> off of the
+ <tref>key stack</tref>.
+ </li>
+ <li>For each <tdef>serialization key</tdef> in the
+ <tref>serialization key info</tref> array, starting at
+ the <tdef>serialization key index</tdef> from the
+ <tref>serialization key info</tref>:
+ <ol class="algorithm">
+ <li>If the <tref>serialization key</tref> is not in the
+ <tref>adjacent info map</tref>, push the
+ <tref>serialization key info</tref> onto the
+ <tref>key stack</tref> and exit from this loop.
+ </li>
+ <li>If the <tref>serialization key</tref> is a key in
+ <tref>serialized keys</tref>, a cycle has been detected. Append
+ the concatenation of the <code>_</code> character and the
+ <tref>serialization key</tref> to the
+ <tref>serialization string</tref>.
+ <li>Otherwise, serialize all outgoing and incoming edges in the
+ related node by performing the following steps:
+ <ol class="algorithm">
+ <li>Mark the <tref>serialization key</tref> as having
+ been processed by adding a new key-value pair to
+ <tref>serialized keys</tref> where the key
+ is the <tref>serialization key</tref> and the value is
+ <code>true</code>.
+ </li>
+ <li>Set the <tdef>serialization fragment</tdef> to the value of
+ the <tref>serialization key</tref>.</li>
+ <li>Set the <tref>adjacent info</tref> to the value of the
+ <tref>serialization key</tref> in the
+ <tref>adjacent info map</tref>.
+ </li>
+ <li>Set the <tref>adjacent node label</tref> to the node
+ <tref>label</tref> from the <tref>adjacent info</tref>.
+ </li>
+ <li>If a mapping for the <tref>adjacent node label</tref>
+ exists in the <tref>map of all labels</tref>:
+ <ol class="algorithm">
+ <li>Append the result of the
+ <a href="">Label Serialization Algorithm</a> to the
+ <tref>serialization fragment</tref>.
+ </li>
+ </ol>
+ </li>
+ <li>Append all of the keys in the <tref>adjacent info</tref>
+ to the <tref>serialization fragment</tref>.
+ </li>
+ <li>Append the <tref>serialization fragment</tref> to the
+ <tref>serialization string</tref>.
+ </li>
+ <li>Push a new key info object containing the keys from the
+ <tref>adjacent info</tref> and an index of <code>0</code>
+ onto the <tref>key stack</tref>.
+ </li>
+ <li>Recursively update the <tref>serialization string</tref>
+ according to the
+ <a href="#mapping-serialization-algorithm">Mapping Serialization Algorithm</a>.
+ </li>
+ </ol>
+ </li>
+ </ol>
+ </li>
+ </ol>
+ </li>
+</ol>
+
+</section>
+
+<section>
+<h4>Label Serialization Algorithm</h4>
+
+<p>
+The label serialization algorithm serializes information about a node that
+has been assigned a particular <tref>serialization label</tref>.
+</p>
+
+<ol class="algorithm">
+ <li>Initialize the <tref>label serialization</tref> to an empty string.</li>
+ <li>Append the <code>[</code> character to the
+ <tref>label serialization</tref>.</li>
+ <li>Append all properties to the <tref>label serialization</tref> by
+ processing each key-value pair in the <tref>node reference</tref>,
+ excluding the
+ <code>@subject</code> property. The keys should be processed in
+ lexicographical order and their associated values should be processed
+ in the order produced by the
+ <a href="#object-comparison-algorithm">Object Comparison Algorithm</a>:
+ <ol class="algorithm">
+ <li>Build a string using the pattern <code><</code><strong>KEY</strong><code>></code>
+ where <strong>KEY</strong> is the current key. Append string to the
+ <tref>label serialization</tref>.</li>
+ <li>The value may be a single object or an array of objects.
+ Process all of the objects that are associated with the key, building
+ an <tdef>object string</tdef> for each item:
+ <ol class="algorithm">
+ <li>If the object contains an <code>@iri</code> key with a
+ value that starts
+ with <code>_:</code>, set the <tref>object string</tref> to
+ the value <code>_:</code>. If the value does not
+ start with <code>_:</code>, build the <tref>object string</tref>
+ using the pattern
+ <code><</code><strong>IRI</strong><code>></code>
+ where <strong>IRI</strong> is the value associated with the
+ <code>@iri</code> key.</li>
+ <li>If the object contains a <code>@literal</code> key and a
+ <code>@datatype</code> key, build the <tref>object string</tref>
+ using the pattern
+ <code>"</code><strong>LITERAL</strong><code>"^^<</code><strong>DATATYPE</strong><code>></code>
+ where <strong>LITERAL</strong> is the value associated with the
+ <code>@literal</code> key and <strong>DATATYPE</strong> is the
+ value associated with the <code>@datatype</code> key.</li>
+ <li>If the object contains a <code>@literal</code> key and a
+ <code>@language</code> key, build the <tref>object string</tref>
+ using the pattern
+ <code>"</code><strong>LITERAL</strong><code>"@</code><strong>LANGUAGE</strong>
+ where <strong>LITERAL</strong> is the value associated with the
+ <code>@literal</code> key and <strong>LANGUAGE</strong> is the
+ value associated with the <code>@language</code> key.</li>
+ <li>Otherwise, the value is a string. Build the
+ <tref>object string</tref> using the pattern
+ <code>"</code><strong>LITERAL</strong><code>"</code>
+ where <strong>LITERAL</strong> is the value associated with the
+ current key.</li>
+ <li>If this is the second iteration of the loop,
+ append a <code>|</code> separator character to the
+ <tref>label serialization</tref>.</li>
+ <li>Append the <tref>object string</tref> to the
+ <tref>label serialization</tref>.</li>
+ </ol>
+ </ol>
+ </li>
+ <li>Append the <code>]</code> character to the
+ <tref>label serialization</tref>.</li>
+ <li>Append the <code>[</code> character to the
+ <tref>label serialization</tref>.</li>
+ <li>Append all incoming references for the current
+ <tref>label</tref> to the <tref>label serialization</tref> by
+ processing all of the items associated with the <tref>incoming list</tref>:
+ <ol class="algorithm">
+ <li>Build a <tdef>reference string</tdef>
+ using the pattern <code><</code><strong>PROPERTY</strong><code>></code><code><</code><strong>REFERER</strong><code>></code>
+ where <strong>PROPERTY</strong> is the property associated with the
+ incoming reference and <strong>REFERER</strong> is either the subject of
+ the node referring to the <tref>label</tref> in the incoming reference
+ or <code>_:</code> if <strong>REFERER</strong> begins with
+ <code>_:</code>.
+ <li>If this is the second iteration of the loop,
+ append a <code>|</code> separator character to the
+ <tref>label serialization</tref>.</li>
+ <li>Append the <tref>reference string</tref> to the
+ <tref>label serialization</tref>.</li>
+ </ol>
+ <li>Append the <code>]</code> character to the
+ <tref>label serialization</tref>.</li>
+ <li>Append all <tref>adjacent node labels</tref> to the
+ <tref>label serialization</tref> by concatenating the string value
+ for all of them, one after the other, to the
+ <tref>label serialization</tref>.</li>
+ <li>Push the <tref>adjacent node labels</tref> onto the
+ <tref>key stack</tref> and append the result of the
+ <a href="#mapping-serialization-algorithm">Mapping Serialization Algorithm</a>
+ to the <tref>label serialization</tref>.
+</ol>
+
+</section>
+
+</section>
+
+<section>
+
+<h3>Data Round Tripping</h3>
+
+<p>When normalizing <strong>xsd:double</strong> values, implementers MUST
+ensure that the normalized value is a string. In order to generate the
+string from a <strong>double</strong> value, output equivalent to the
+<code>printf("%1.6e", value)</code> function in C MUST be used where
+<strong>"%1.6e"</strong> is the string formatter and <strong>value</strong>
+is the value to be converted.</p>
+
+<p>To convert the a double value in JavaScript, implementers can use the
+following snippet of code:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+// the variable 'value' below is the JavaScript native double value that is to be converted
+(value).toExponential(6).replace(/(e(?:\+|-))([0-9])$/, '$10$2')
+-->
+</pre>
+
+<p class="note">When data needs to be normalized, JSON-LD authors should
+not use values that are going to undergo automatic conversion. This is due
+to the lossy nature of <strong>xsd:double</strong> values.</p>
+
+<p class="note">Some JSON serializers, such as PHP's native implementation,
+backslash-escapes the forward slash character. For example, the value
+<code>http://example.com/</code> would be serialized as
+<code>http:\/\/example.com\/</code> in some
+versions of PHP. This is problematic when generating a byte
+stream for processes such as normalization. There is no need to
+backslash-escape forward-slashes in JSON-LD. To aid interoperability between
+JSON-LD processors, a JSON-LD serializer MUST NOT backslash-escape
+forward slashes.</p>
+
+<p class="issue">Round-tripping data can be problematic if we mix and
+match @coerce rules with JSON-native datatypes, like integers. Consider the
+following code example:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+var myObj = { "@context" : {
+ "number" : "http://example.com/vocab#number",
+ "@coerce": {
+ "xsd:nonNegativeInteger": "number"
+ }
+ },
+ "number" : 42 };
+
+// Map the language-native object to JSON-LD
+var jsonldText = jsonld.normalize(myObj);
+
+// Convert the normalized object back to a JavaScript object
+var myObj2 = jsonld.parse(jsonldText);
+-->
+</pre>
+
+<p class="issue">At this point, myObj2 and myObj will have different
+values for the "number" value. myObj will be the number 42, while
+myObj2 will be the string "42". This type of data round-tripping
+error can bite developers. We are currently wondering if having a
+"coerce validation" phase in the parsing/normalization phases would be a
+good idea. It would prevent data round-tripping issues like the
+one mentioned above.</p>
+
+</section>
+
+<section>
+<h2>RDF Conversion</h2>
+
+<p>A JSON-LD document MAY be converted to any other RDF-compatible document
+format using the algorithm specified in this section.</p>
+
+<p>
+ The JSON-LD Processing Model describes processing rules for extracting RDF
+ from a JSON-LD document. Note that many uses of JSON-LD may not require
+ generation of RDF.
+</p>
+
+<p>
+The processing algorithm described in this section is provided in
+order to demonstrate how one might implement a JSON-LD to RDF processor.
+Conformant implementations are only required to produce the same type and
+number of triples during the output process and are not required to
+implement the algorithm exactly as described.
+</p>
+
+<p class="issue">The RDF Conversion Algorithm is a work in progress.</p>
+
+<section class="informative">
+ <h4>Overview</h4>
+ <p>
+ JSON-LD is intended to have an easy to parse grammar that closely models existing
+ practice in using JSON for describing object representations. This allows the use
+ of existing libraries for parsing JSON.
+ </p>
+ <p>
+ As with other grammars used for describing <tref>Linked Data</tref>, a key concept is that of
+ a <em>resource</em>. Resources may be of three basic types: <em>IRI</em>s, for describing
+ externally named entities, <em>BNodes</em>, resources for which an external name does not
+ exist, or is not known, and Literals, which describe terminal entities such as strings,
+ dates and other representations having a lexical representation possibly including
+ an explicit language or datatype.
+ </p>
+ <p>
+ Data described with JSON-LD may be considered to be the representation of a graph made
+ up of <tref>subject</tref> and <tref>object</tref> resources related via a <tref>property</tref> resource.
+ However, specific implementations may choose to operate on the document as a normal
+ JSON description of objects having attributes.
+ </p>
+</section>
+
+<section>
+ <h4>RDF Conversion Algorithm Terms</h4>
+ <dl>
+ <dt><tdef>default graph</tdef></dt>
+ <dd>
+ the destination graph for all triples generated by JSON-LD markup.
+ </dd>
+ </dl>
+</section>
+
+<section>
+ <h3>RDF Conversion Algorithm</h3>
+ <p>
+ The algorithm below is designed for in-memory implementations with random access to <tref>JSON object</tref> elements.
+ </p>
+ <p>
+ A conforming JSON-LD processor implementing RDF conversion MUST implement a
+ processing algorithm that results in the same <tref>default graph</tref> that the following
+ algorithm generates:
+ </p>
+
+ <ol class="algorithm">
+ <li id="processing-step-default-context">
+ Create a new <tref>processor state</tref> with with the <tref>active context</tref> set to the
+ <tref>initial context</tref> and <tref>active subject</tref> and <tref>active property</tref>
+ initialized to NULL.
+ </li>
+
+ <li id="processing-step-associative">
+ If a <tref>JSON object</tref> is detected, perform the following steps:
+ <ol class="algorithm">
+ <li>
+ If the <tref>JSON object</tref> has a <code>@context</code> key, process the local context as
+ described in <a href="#context">Context</a>.
+ </li>
+ <li>
+ Create a new <tref>JSON object</tref> by mapping the keys from the current <tref>JSON object</tref> using the
+ <tref>active context</tref> to new keys using the associated value from the current <tref>JSON object</tref>.
+ Repeat the mapping until no entry is found within the <tref>active context</tref> for the key. Use the new
+ <tref>JSON object</tref> in subsequent steps.
+ </li>
+ <li>
+ If the <tref>JSON object</tref> has an <code>@iri</code> key, set the <tref>active object</tref> by
+ performing <a href="#iri-expansion">IRI Expansion</a> on the associated value. Generate a
+ triple representing the <tref>active subject</tref>, the <tref>active property</tref> and the
+ <tref>active object</tref>. Return the <tref>active object</tref> to the calling location.
+ <p class="issue"><code>@iri</code> really just behaves the same as <code>@subject</code>, consider consolidating them.</p>
+ </li>
+ <li>
+ If the <tref>JSON object</tref> has a <code>@literal</code> key, set the <tref>active object</tref>
+ to a literal value as follows:
+ <ol class="algorithm">
+ <li>
+ as a <tref>typed literal</tref> if the <tref>JSON object</tref> contains a <code>@datatype</code> key
+ after performing <a href="#iri-expansion">IRI Expansion</a> on the specified<code>@datatype</code>.
+ </li>
+ <li>
+ otherwise, as a <tref>plain literal</tref>. If the <tref>JSON object</tref> contains
+ a <code>@language</code> key, use it's value to set the language of the plain literal.
+ </li>
+ <li>
+ Generate a triple representing the <tref>active subject</tref>, the <tref>active property</tref> and the
+ <tref>active object</tref>. Return the <tref>active object</tref> to the calling location.
+ </li>
+ </ol>
+ </li>
+ <li id="processing-step-subject">If the <tref>JSON object</tref> has a <code>@subject</code> key:
+ <ol class="algorithm">
+ <li>
+ If the value is a <tref>string</tref>, set the <tref>active object</tref> to the result of performing
+ <a href="#iri-expansion">IRI Expansion</a>. Generate a
+ triple representing the <tref>active subject</tref>, the <tref>active property</tref> and the
+ <tref>active object</tref>. Set the <tref>active subject</tref> to the <tref>active object</tref>.
+ </li>
+ <li>
+ Create a new <tref>processor state</tref> using copies of the <tref>active context</tref>,
+ <tref>active subject</tref> and <tref>active property</tref> and process the value
+ starting at <a href="#processing-step-associative">Step 2</a>, set the <tref>active
+ subject</tref> to the result and proceed using the previous <tref>processor state</tref>.
+ </li>
+ </ol>
+ </li>
+ <li>
+ If the <tref>JSON object</tref> does not have a <code>@subject</code> key, set the <tref>active
+ object</tref> to newly generated <tdef>blank node identifier</tdef>. Generate a triple
+ representing the <tref>active subject</tref>, the <tref>active property</tref> and the
+ <tref>active object</tref>. Set the <tref>active subject</tref> to the <tref>active
+ object</tref>.
+ </li>
+ <li>
+ For each key in the <tref>JSON object</tref> that has not already been processed, perform
+ the following steps:
+ <ol class="algorithm">
+ <li>
+ If the key is <code>@type</code>, set the <tref>active property</tref>
+ to <code>rdf:type</code>.
+ </li>
+ <li>Otherwise, set the <tref>active property</tref> to the result of performing
+ <a href="#iri-expansion">IRI Expansion</a> on the key.</li>
+ <li>
+ Create a new <tref>processor state</tref> copies of the <tref>active context</tref>,
+ <tref>active subject</tref> and <tref>active property</tref> and process the value
+ starting at <a href="#processing-step-associative">Step 2</a> and proceed using the
+ previous <tref>processor state</tref>.
+ </li>
+ </ol>
+ </li>
+ <li>
+ Return the <tref>active object</tref> to the calling location.
+ </li>
+ </ol>
+ </li>
+
+ <li>
+ If a regular <tref>array</tref> is detected, process each value in the <tref>array</tref> by doing the following
+ returning the result of processing the last value in the <tref>array</tref>:
+
+ <ol class="algorithm">
+ <li>
+ Create a new <tref>processor state</tref> using copies of the <tref>active
+ context</tref>, <tref>active subject</tref> and <tref>active property</tref> and process the value
+ starting at <a href="#processing-step-associative">Step 2</a> then proceed using the previous
+ <tref>processor state</tref>.
+ </li>
+ </ol>
+ </li>
+
+ <li>
+ If a <tref>string</tref> is detected:
+ <ol class="algorithm">
+ <li>
+ If the <tref>active property</tref> is the target of a <code>@iri</code> coercion,
+ set the <tref>active object</tref> by
+ performing <a href="#iri-expansion">IRI Expansion</a> on the string.
+ </li>
+ <li>
+ Otherwise, if the <tref>active property</tref> is the target of coercion,
+ set the <tref>active object</tref> by creating a <tref>typed literal</tref> using
+ the string and the coercion key as the datatype IRI.
+ </li>
+ <li>
+ Otherwise, set the <tref>active object</tref> to a <tref>plain literal</tref> value created from
+ the string.
+ </li>
+ </ol>
+ Generate a
+ triple representing the <tref>active subject</tref>, the <tref>active property</tref> and the
+ <tref>active object</tref>.
+ </li>
+
+ <li>
+ If a <tref>number</tref> is detected, generate a <tref>typed literal</tref> using a string representation of
+ the value with datatype set to either <code>xsd:integer</code> or
+ <code>xsd:double</code>, depending on if the value contains a
+ fractional and/or an exponential component. Generate a triple using the <tref>active
+ subject</tref>, <tref>active property</tref> and the generated typed literal.
+ </li>
+
+ <li>
+ Otherwise, if <strong>true</strong> or <strong>false</strong> is detected,
+ generate a triple using the <tref>active subject</tref>, <tref>active property</tref>
+ and a <tref>typed literal</tref> value created from the string representation of the
+ value with datatype set to <code>xsd:boolean</code>.
+ </li>
+ </ol>
+</section>
+
+<!-- THIS SHOULD BE SPLIT OUT INTO A SEPARATE DOCUMENT
+
+<section>
+<h1>Best Practices</h1>
+
+<p>The nature of Web programming allows one to use basic technologies, such as
+JSON-LD, across a variety of systems and environments. This section attempts to
+describe some of those environments and the way in which JSON-LD can be
+integrated in order to help alleviate certain development headaches.
+</p>
+
+<section>
+<h2>JavaScript</h2>
+
+<p class="issue">It is expected that JSON-LD will be used quite a bit in
+JavaScript environments, however, features like the expanded form for
+object values mean that using JSON-LD directly in JavaScript may be
+annoying without a middleware layer such as a simple library that
+converts JSON-LD markup before JavaScript uses it. One could say that JSON-LD
+is a good fit for the RDF API, which enables a variety of RDF-based
+Web Applications, but some don't want to require that level of functionality
+just to use JSON-LD. The group is still discussing the best way to proceed,
+so input on how JSON-LD could more easily be utilized in JavaScript
+environments would be very much appreciated.
+</p>
+</section>
+
+<section>
+<h2>Schema-less Databases</h2>
+
+<p class="issue">Databases such as CouchDB and MongoDB allow the creation of
+schema-less data stores. RDF is a type of schema-less data model and thus
+lends itself to databases such as CouchDB and MongoDB. Both of these databases
+can use JSON-LD as their storage format. The group needs feedback from
+CouchDB and MongoDB experts regarding the usefulness of JSON-LD in those
+environments.</p>
+
+<p class="issue">MongoDB does not allow the '.' character to be used in
+key names. This prevents developers from storing IRIs as keys, which also
+prevents storage of the data in normalized form. While this issue can
+be avoided by using <tref>prefix</tref>es for key values, it is not known if this
+mechanism is enough to allow JSON-LD to be used in MongoDB in a way that
+is useful to developers.
+</p>
+
+-->
+</section>
+
+</section>
+
+<section class="appendix">
+<h1>Experimental Concepts</h1>
+
+<p class="issue">There are a few advanced concepts where it is not clear
+whether or not the JSON-LD specification is going to support the complexity
+necessary to support each concept. The entire section on Advanced Concepts
+should be considered as discussion points; it is merely a list of
+possibilities where all of the benefits and drawbacks have not been explored.
+</p>
+
+<section>
+<h2>Disjoint Graphs</h2>
+
+<p>When serializing an RDF graph that contains two or more sections of the
+graph which are entirely disjoint, one must use an <tref>array</tref> to express the graph
+as two graphs. This may not be acceptable to some authors, who would rather
+express the information as one graph. Since, by definition, disjoint graphs
+require there to be two top-level objects, JSON-LD utilizes a mechanism that
+allows disjoint graphs to be expressed using a single graph.</p>
+
+<p>Assume the following RDF graph:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+<http://example.org/people#john>
+ <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
+ <http://xmlns.com/foaf/0.1/Person> .
+<http://example.org/people#jane>
+ <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
+ <http://xmlns.com/foaf/0.1/Person> .
+-->
+</pre>
+
+<p>Since the two subjects are entirely disjoint with one another, it is
+impossible to express the RDF graph above using a single <tref>JSON object</tref>.</p>
+
+<p>In JSON-LD, one can use the subject to express disjoint graphs as a
+single graph:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "@context": {
+ "Person": "http://xmlns.com/foaf/0.1/Person"
+ },
+ "@subject":
+ [
+ {
+ "@subject": "http://example.org/people#john",
+ "@type": "Person"
+ },
+ {
+ "@subject": "http://example.org/people#jane",
+ "@type": "Person"
+ }
+ ]
+}
+-->
+</pre>
+
+<p>A disjoint graph could also be expressed like so:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+[
+ {
+ "@subject": "http://example.org/people#john",
+ "@type": "http://xmlns.com/foaf/0.1/Person"
+ },
+ {
+ "@subject": "http://example.org/people#jane",
+ "@type": "http://xmlns.com/foaf/0.1/Person"
+ }
+]
+-->
+</pre>
+
+<p class="note">Warning: Using this serialisation format it is impossible to include <code>@context</code>
+ given that the document's data structure is an array and not an object.</p>
+
+</section>
+
+<section>
+ <h2>Lists</h2>
+ <p>
+ Because graphs do not describe ordering for links between nodes, in contrast to plain JSON, multi-valued properties
+ in JSON-LD do not provide an ordering of the listed objects. For example, consider the following
+ simple document:
+ </p>
+ <pre class="example" data-transform="updateExample">
+ <!--
+ {
+ ...
+ "@subject": "http://example.org/people#joebob",
+ "nick": ****["joe", "bob", "jaybee"]****,
+ ...
+ }
+ -->
+ </pre>
+ <p>
+ This results in three triples being generated, each relating the subject to an individual
+ object, with no inherent order.</p>
+ <p>To preserve the order of the objects, RDF-based languages, such as [[TURTLE]]
+ use the concept of an <code>rdf:List</code> (as described in [[RDF-SCHEMA]]). This uses a sequence
+ of unlabeled nodes with properties describing a value, a null-terminated next property. Without
+ specific syntactical support, this could be represented in JSON-LD as follows:
+ </p>
+ <pre class="example" data-transform="updateExample">
+ <!--
+ {
+ ...
+ "@subject": "http://example.org/people#joebob",
+ "nick": ****{****,
+ ****"@first": "joe"****,
+ ****"@rest": {****
+ ****"@first": "bob"****,
+ ****"@rest": {****
+ ****"@first": "jaybee"****,
+ ****"@rest": "@nil"****
+ ****}****
+ ****}****
+ ****}****
+ ****}****,
+ ...
+ }
+ -->
+ </pre>
+ <p>
+ As this notation is rather unwieldy and the notion of ordered collections is rather important
+ in data modeling, it is useful to have specific language support. In JSON-LD, a list may
+ be represented using the <code>@list</code> keyword as follows:
+ </p>
+ <pre class="example" data-transform="updateExample">
+ <!--
+ {
+ ...
+ "@subject": "http://example.org/people#joebob",
+ "foaf:nick": ****{"@list": ["joe", "bob", "jaybee"]}****,
+ ...
+ }
+ -->
+ </pre>
+ <p>
+ This describes the use of this <tref>array</tref> as being ordered, and order is maintained through
+ normalization and RDF conversion. If every use of a given multi-valued property is a
+ list, this may be abbreviated by adding an <code>@coerce</code> term:
+ </p>
+ <pre class="example" data-transform="updateExample">
+ <!--
+ {
+ ****"@context": {****
+ ...
+ ****"@coerce": {****
+ ****"@list": ["foaf:nick"]****
+ ****}****
+ ****}****,
+ ...
+ "@subject": "http://example.org/people#joebob",
+ "foaf:nick": ****["joe", "bob", "jaybee"]****,
+ ...
+ }
+ -->
+ </pre>
+ <p class="issue">There is an ongoing discussion about this issue. One of the <a href="https://github.com/json-ld/json-ld.org/issues/12">proposed solutions</a> is allowing to change the default behaviour so that arrays are considered as ordered lists by default.</p>
+ <section><h3 id="list-expansion">Expansion</h3>
+ <p class="issue">TBD.</p>
+ </section>
+ <section><h3 id="list-normalization">Normalization</h3>
+ <p class="issue">TBD.</p>
+ </section>
+ <section><h3 id="list-rdf">RDF Conversion</h3>
+ <p>
+ To support RDF Conversion of lists, <a href="#rdf-conversion-algorithm">RDF Conversion Algorithm</a>
+ is updated as follows:
+ </p>
+ <ol class="algorithm update">
+ <li>
+ <span class="list-number">2.4a.</span>
+ If the <tref>JSON object</tref> has a <code>@list</code> key and the value is an <tref>array</tref>
+ process the value as a list starting at <a href="#processing-step-list">Step 3a</a>.
+ </li>
+ <li>
+ <span class="list-number">2.7.3.</span>
+ Create a new <tref>processor state</tref> copies of the <tref>active context</tref>,
+ <tref>active subject</tref> and <tref>active property</tref>.
+ <ol class="algorithm">
+ <li>
+ If the <tref>active property</tref> is the target of a <code>@list</code> coercion,
+ and the value is an <tref>array</tref>,
+ process the value as a list starting at <a href="#processing-step-list">Step 3a</a>.
+ </li>
+ <li>
+ Otherwise, process the value starting at
+ <a href="#processing-step-associative">Step 2</a>.
+ </li>
+ <li>Proceed using the previous <tref>processor state</tref>.</li>
+ </ol>
+ </li>
+ <li id="processing-step-list">
+ <span class="list-number">3a.</span>
+ Generate an RDF List by linking
+ each element of the list using <code>rdf:first</code> and <code>rdf:next</code>, terminating the list with <code>rdf:nil</code>
+ using the following sequence:
+ <ol class="algorithm">
+ <li>
+ If the list has no element, generate a triple using the <tref>active subject</tref>, <tref>active property</tref>
+ and <code>rdf:nil</code>.
+ </li>
+ <li>
+ Otherwise, generate a triple using using the <tref>active subject</tref>, <tref>active property</tref>
+ and a newly generated BNode identified as <em>first <tdef>blank node identifier</tdef></em>.
+ </li>
+ <li>
+ For each element other than the last element in the list:
+ <ol class="algorithm">
+ <li>Create a processor state using the active context, <em>first <tdef>blank node identifier</tdef></em> as the <tref>active subject</tref>, and <code>rdf:first</code> as the <tref>active property</tref>.</li>
+ <li>Unless this is the last element in the list, generate a new BNode identified as <em>rest <tdef>blank node identifier</tdef></em>, otherwise use <code>rdf:nil</code>.</li>
+ <li>Generate a new triple using <em>first <tdef>blank node identifier</tdef></em>, <code>rdf:rest</code> and <em>rest <tdef>blank node identifier</tdef></em>.</li>
+ <li>Set <em>first <tdef>blank node identifier</tdef></em> to <em>rest <tdef>blank node identifier</tdef></em>.</li>
+ </ol>
+ </li>
+ </ol>
+ </li>
+ </ol>
+ </section>
+</section>
+
+</section>
+
+<section class="appendix">
+<h2>Markup Examples</h2>
+
+<p>The JSON-LD markup examples below demonstrate how JSON-LD can be used to
+express semantic data marked up in other languages such as RDFa, Microformats,
+and Microdata. These sections are merely provided as proof that JSON-LD is
+very flexible in what it can express across different Linked Data approaches.
+</p>
+
+<section>
+<h3>RDFa</h3>
+
+<p>The following example describes three people with their respective names and
+homepages.</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+<div ****prefix="foaf: http://xmlns.com/foaf/0.1/"****>
+ <ul>
+ <li ****typeof="foaf:Person"****>
+ <a ****rel="foaf:homepage" href="http://example.com/bob/" property="foaf:name" ****>Bob</a>
+ </li>
+ <li ****typeof="foaf:Person"****>
+ <a ****rel="foaf:homepage" href="http://example.com/eve/" property="foaf:name" ****>Eve</a>
+ </li>
+ <li ****typeof="foaf:Person"****>
+ <a ****rel="foaf:homepage" href="http://example.com/manu/" property="foaf:name" ****>Manu</a>
+ </li>
+ </ul>
+</div>
+-->
+</pre>
+
+<p>An example JSON-LD implementation is described below, however, there are
+other ways to mark-up this information such that the context is not
+repeated.</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "@context": { "foaf": "http://xmlns.com/foaf/0.1/"},
+ "@subject": [
+ {
+ "@subject": "_:bnode1",
+ "@type": "foaf:Person",
+ "foaf:homepage": "http://example.com/bob/",
+ "foaf:name": "Bob"
+ },
+ {
+ "@subject": "_:bnode2",
+ "@type": "foaf:Person",
+ "foaf:homepage": "http://example.com/eve/",
+ "foaf:name": "Eve"
+ },
+ {
+ "@subject": "_:bnode3",
+ "@type": "foaf:Person",
+ "foaf:homepage": "http://example.com/manu/",
+ "foaf:name": "Manu"
+ }
+ ]
+}
+-->
+</pre>
+
+</section>
+
+<section>
+<h3>Microformats</h3>
+
+<p>The following example uses a simple Microformats hCard example to express
+how the Microformat is represented in JSON-LD.</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+<div class="vcard">
+ <a class="url fn" href="http://tantek.com/">Tantek Çelik</a>
+</div>
+-->
+</pre>
+
+<p>The representation of the hCard expresses the Microformat terms in the
+context and uses them directly for the <code>url</code> and <code>fn</code>
+properties. Also note that the Microformat to JSON-LD processor has
+generated the proper URL type for <code>http://tantek.com</code>.</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "@context":
+ {
+ "vcard": "http://microformats.org/profile/hcard#vcard",
+ "url": "http://microformats.org/profile/hcard#url",
+ "fn": "http://microformats.org/profile/hcard#fn",
+ "@coerce": { "@iri": "url" }
+ },
+ "@subject": "_:bnode1",
+ "@type": "vcard",
+ "url": "http://tantek.com/",
+ "fn": "Tantek Çelik"
+}
+-->
+</pre>
+
+</section>
+
+<section>
+<h3>Microdata</h3>
+
+<p>The Microdata example below expresses book information as a Microdata Work
+item.
+</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+<dl itemscope
+ itemtype="http://purl.org/vocab/frbr/core#Work"
+ itemid="http://purl.oreilly.com/works/45U8QJGZSQKDH8N">
+ <dt>Title</dt>
+ <dd><cite itemprop="http://purl.org/dc/terms/title">Just a Geek</cite></dd>
+ <dt>By</dt>
+ <dd><span itemprop="http://purl.org/dc/terms/creator">Wil Wheaton</span></dd>
+ <dt>Format</dt>
+ <dd itemprop="http://purl.org/vocab/frbr/core#realization"
+ itemscope
+ itemtype="http://purl.org/vocab/frbr/core#Expression"
+ itemid="http://purl.oreilly.com/products/9780596007683.BOOK">
+ <link itemprop="http://purl.org/dc/terms/type" href="http://purl.oreilly.com/product-types/BOOK">
+ Print
+ </dd>
+ <dd itemprop="http://purl.org/vocab/frbr/core#realization"
+ itemscope
+ itemtype="http://purl.org/vocab/frbr/core#Expression"
+ itemid="http://purl.oreilly.com/products/9780596802189.EBOOK">
+ <link itemprop="http://purl.org/dc/terms/type" href="http://purl.oreilly.com/product-types/EBOOK">
+ Ebook
+ </dd>
+</dl>
+-->
+</pre>
+
+<p>Note that the JSON-LD representation of the Microdata information stays
+true to the desires of the Microdata community to avoid contexts and
+instead refer to items by their full IRI.</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+[
+ {
+ "@subject": "http://purl.oreilly.com/works/45U8QJGZSQKDH8N",
+ "@type": "http://purl.org/vocab/frbr/core#Work",
+ "http://purl.org/dc/terms/title": "Just a Geek",
+ "http://purl.org/dc/terms/creator": "Whil Wheaton",
+ "http://purl.org/vocab/frbr/core#realization":
+ ["http://purl.oreilly.com/products/9780596007683.BOOK", "http://purl.oreilly.com/products/9780596802189.EBOOK"]
+ },
+ {
+ "@subject": "http://purl.oreilly.com/products/9780596007683.BOOK",
+ "@type": "http://purl.org/vocab/frbr/core#Expression",
+ "http://purl.org/dc/terms/type": "http://purl.oreilly.com/product-types/BOOK"
+ },
+ {
+ "@subject": "http://purl.oreilly.com/products/9780596802189.EBOOK",
+ "@type": "http://purl.org/vocab/frbr/core#Expression",
+ "http://purl.org/dc/terms/type": "http://purl.oreilly.com/product-types/EBOOK"
+ }
+]
+-->
+</pre>
+</section>
+</section>
+
+<section class="appendix">
+<h3>Mashing Up Vocabularies</h3>
+
+<p>Developers would also benefit by allowing other vocabularies to be used
+automatically with their JSON API. There are over 200
+<tref>Web Vocabulary</tref> Documents that are available for use on the Web
+today. Some of these vocabularies are:
+</p>
+
+<ul>
+ <li>RDF - for describing information about objects and concepts on the Web.</li>
+ <li>RDFS - for expressing things like labels and comments.</li>
+ <li>XSD - for specifying basic types like strings, integers, dates and times.</li>
+ <li>Dublin Core - for describing creative works.</li>
+ <li>FOAF - for describing social networks.</li>
+ <li>Calendar - for specifying events.</li>
+ <li>SIOC - for describing discussions on blogs and websites.</li>
+ <li>CCrel - for describing Creative Commons and other types of licenses.</li>
+ <li>GEO - for describing geographic location.</li>
+ <li>VCard - for describing organizations and people.</li>
+ <li>DOAP - for describing projects.</li>
+</ul>
+
+<p>You can use these vocabularies in combination, like so:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ "****@type****": "****foaf:Person****",
+ "****foaf:name****": "Manu Sporny",
+ "****foaf:homepage****": "http://manu.sporny.org/",
+ "****sioc:avatar****": "http://twitter.com/account/profile_image/manusporny"
+}
+-->
+</pre>
+
+<p>Developers can also specify their own Vocabulary documents by modifying the
+<tref>active context</tref> in-line using the <code>@context</code> keyword,
+like so:</p>
+
+<pre class="example" data-transform="updateExample">
+<!--
+{
+ ****"@context": { "myvocab": "http://example.org/myvocab#" }****,
+ "@type": "foaf:Person",
+ "foaf:name": "Manu Sporny",
+ "foaf:homepage": "http://manu.sporny.org/",
+ "sioc:avatar": "http://twitter.com/account/profile_image/manusporny"****,
+ "myvocab:personality": "friendly"****
+}
+
+-->
+</pre>
+
+<p>The <code>@context</code> keyword is used to change how the JSON-LD
+processor evaluates key-value pairs. In this case, it was used to
+map one string ('myvocab') to another string, which is interpreted as
+a <tref>IRI</tref>. In the example above, the <code>myvocab</code> string is replaced
+with "<code>http://example.org/myvocab#</code>" when it
+is detected. In the example above, "<code>myvocab:personality</code>" would
+expand to "<code>http://example.org/myvocab#personality</code>".</p>
+
+<p>This mechanism is a short-hand, called a <tref>Web Vocabulary</tref> <tref>prefix</tref>,
+and provides developers an unambiguous way to map any JSON value to RDF.<p>
+
+</section>
+
+<section class="appendix">
+<h1>IANA Considerations</h1>
+
+<p>This section is included merely for standards community review and will be
+submitted to the Internet Engineering Steering Group if this specification
+becomes a W3C Recommendation.</p>
+
+<dl>
+ <dt>Type name:</dt>
+ <dd>application</dd>
+ <dt>Subtype name:</dt>
+ <dd>ld+json</dd>
+ <dt>Required parameters:</dt>
+ <dd>None</dd>
+ <dt>Optional parameters:</dt>
+ <dd>
+ <dl>
+ <dt><code>form</code></dt>
+ <dd>Determines the serialization form for the JSON-LD document. Valid
+ values include; <code>compacted</code>, <code>expanded</code>,
+ <code>framed</code>, and <code>normalized</code>. Other values are
+ allowed, but must be pre-pended with a <code>x-</code> string until
+ they are clearly defined by a stable specification. If no form
+ is specified in an HTTP request header to a responding application,
+ such as a Web server, the application MAY choose any form. If no
+ form is specified for a receiving application, the form MUST NOT
+ be assumed to take any particular form.</dd>
+ <div class="issue">It is currently <a href="https://github.com/json-ld/json-ld.org/issues/14"> being discussed to remove form=framed</a> from this specification as there are several issues with it.</div>
+ </dl>
+ </dd>
+ <dt>Encoding considerations:</dt>
+ <dd>The same as the <code>application/json</code> MIME media type.</dd>
+ <dt>Security considerations:</dt>
+ <dd>Since JSON-LD is intended to be a pure data exchange format for
+ directed graphs, the serialization SHOULD NOT be passed through a
+ code execution mechanism such as JavaScript's <code>eval()</code>
+ function. It is RECOMMENDED that a conforming parser does not attempt to
+ directly evaluate the JSON-LD serialization and instead purely parse the
+ input into a language-native data structure. </dd>
+ <dt>Interoperability considerations:</dt>
+ <dd>Not Applicable</dd>
+ <dt>Published specification:</dt>
+ <dd>The <a href="http://json-ld/spec/latest/">JSON-LD</a> specification.</dd>
+ <dt>Applications that use this media type:</dt>
+ <dd>Any programming environment that requires the exchange of
+ directed graphs. Implementations of JSON-LD have been created for
+ JavaScript, Python, Ruby, PHP and C++.
+ </dd>
+ <dt>Additional information:</dt>
+ <dd>
+ <dl>
+ <dt>Magic number(s):</dt>
+ <dd>Not Applicable</dd>
+ <dt>File extension(s):</dt>
+ <dd>.jsonld</dd>
+ <dt>Macintosh file type code(s):</dt>
+ <dd>TEXT</dd>
+ </dl>
+ </dd>
+ <dt>Person & email address to contact for further information:</dt>
+ <dd>Manu Sporny <msporny@digitalbazaar.com></dd>
+ <dt>Intended usage:</dt>
+ <dd>Common</dd>
+ <dt>Restrictions on usage:</dt>
+ <dd>None</dd>
+ <dt>Author(s):</dt>
+ <dd>Manu Sporny, Gregg Kellogg, Dave Longley</dd>
+ <dt>Change controller:</dt>
+ <dd>W3C</dd>
+</dl>
+
+</section>
+
+<section class="appendix">
+<h1>Acknowledgements</h1>
+
+<p>The editors would like to thank Mark Birbeck, who provided a great deal of
+the initial push behind the JSON-LD work via his work on RDFj,
+Dave Longley, Dave Lehn and Mike Johnson who reviewed, provided feedback, and
+performed several implementations of the specification, and Ian Davis, who
+created RDF/JSON. Thanks also to Nathan Rixham, Bradley P. Allen,
+Kingsley Idehen, Glenn McDonald, Alexandre Passant, Danny Ayers, Ted
+Thibodeau Jr., Olivier Grisel, Niklas Lindström, Markus Lanthaler, and Richard
+Cyganiak for their input on the specification. Another huge thank you goes out
+to Dave Longley who designed many of the algorithms used in this specification,
+including the normalization algorithm which was a monumentally difficult
+design challenge.
+</p>
+</section>
+
+</body>
+</html>
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
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@@ -0,0 +1,4 @@
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+ol.algorithm li { margin: 0.5em 0; }
+ol.algorithm li:before { font-weight: bold; counter-increment: numsection; content: counters(numsection, ".") ") "; }
+
--- a/spec/latest/spec.css Fri Oct 14 17:34:09 2011 -0400
+++ /dev/null Thu Jan 01 00:00:00 1970 +0000
@@ -1,4 +0,0 @@
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