--- a/rdf-concepts/index.html Wed Jan 09 08:58:34 2013 -0800
+++ b/rdf-concepts/index.html Sun Jan 13 20:39:46 2013 +0000
@@ -152,7 +152,7 @@
including:</p>
<ul>
- <li>Serialization syntaxes for storing and exchanging RDF
+ <li>serialization syntaxes for storing and exchanging RDF
(e.g., <a href="http://www.w3.org/TR/turtle/">Turtle</a> [[TURTLE-TR]]
and <a href="http://www.w3.org/TR/REC-rdf-syntax/">RDF/XML</a>
[[RDF-SYNTAX-GRAMMAR]]),</li>
@@ -161,27 +161,27 @@
Query Language</a> [[RDF-SPARQL-QUERY]],</li>
<li>the <a href="http://www.w3.org/TR/rdf-schema/">RDF Vocabulary
- Description Language</a> [[RDF-SCHEMA]],</li>
+ Description Language</a> (RDFS) [[RDF-SCHEMA]],</li>
- <li>a <a href="http://www.w3.org/TR/rdf-mt/">formal
- model-theoretic semantics for RDF</a> [[RDF-MT]].</li>
+ <li>the <a href="http://www.w3.org/TR/rdf-mt/">formal
+ model-theoretic semantics for RDF and RDFS</a> [[RDF-MT]].</li>
</ul>
<section id="data-model">
<h3>Graph-based Data Model</h3>
- <p>The core structure of the abstract syntax is a collection of
+ <p>The core structure of the abstract syntax is a set of
<a title="RDF triple">triples</a>, each consisting of a <a>subject</a>,
a <a>predicate</a> and an <a>object</a>. A set of such triples is called
- an <a>RDF graph</a>. This can be illustrated by a node and
+ an <a>RDF graph</a>. An RDF graph can be visualized as a node and
directed-arc diagram, in which each triple is represented as a
- node-arc-node link; hence the term “graph”.</p>
+ node-arc-node link.</p>
<div class="figure">
<a href="rdf-graph.png"><img src="rdf-graph.svg" alt="An RDF graph with two nodes (Subject and Object) and a triple connecting them (Predicate)" /></a>
</div>
- <p>There may be three kinds of <a title="node">nodes</a> in an
+ <p>There can be three kinds of <a title="node">nodes</a> in an
<a>RDF graph</a>: <a title="IRI">IRIs</a>, <a title="literal">literals</a>,
and <a title="blank node">blank nodes</a>.</p>
</section>
@@ -190,7 +190,7 @@
<section id="resources-and-statements">
<h3>Resources and Statements</h3>
- <p>Any <a>IRI</a> and <a>literal</a> <dfn title="denote">denotes</dfn>
+ <p>Any <a>IRI</a> or <a>literal</a> <dfn title="denote">denotes</dfn>
some thing in the universe of discourse. These things are called
<dfn title="resource">resources</dfn>. Anything can be a resource,
including physical things, documents, abstract concepts, numbers
@@ -229,7 +229,10 @@
<p>The <a>resource</a> <a title="denote">denoted</a> by an <a>IRI</a>
is also called its <dfn>referent</dfn>.
What exactly is denoted by any given IRI is not defined by this
- specification. The question is treated in other documents like
+ specification.</p>
+
+ <p>Guidelines for determining the <a>referent</a> of an <a>IRI</a> are
+ provided in other documents, like
<em><a href="http://www.w3.org/TR/webarch/">Architecture of the
World Wide Web, Volume One</a></em> [[WEBARCH]] and
<em><a href="http://www.w3.org/TR/cooluris/">Cool URIs for the
@@ -247,11 +250,13 @@
<li>The IRI owner can establish the intended <a>referent</a>
by means of a specification or other document that explains
- what is denoted. For example, [[RDF-SCHEMA]] specifies the referents
+ what is denoted. For example, the
+ <a href="http://www.w3.org/TR/vocab-org/">Organization Ontology
+ document</a> [[VOCAB-ORG]] specifies the referents
of various IRIs that start with
- <code>http://www.w3.org/2000/01/rdf-schema#</code>.</li>
+ <code>http://www.w3.org/ns/org#</code>.</li>
- <li>A good way of communicating the intended referent to the world
+ <li>A good way of communicating the intended referent
is to set up the IRI so that it
<a href="http://www.w3.org/TR/webarch/#uri-dereference">dereferences</a>
[[WEBARCH]] to such a document.</li>
@@ -362,7 +367,7 @@
<section id="managing-graphs">
- <h3>Working with Multiple RDF Graphs and G-Boxes</h3>
+ <h3>Working with Multiple RDF Graphs</h3>
<p>As RDF graphs are sets of triples, they can be
<a title="merge">merged</a> easily, supporting the use of data from
@@ -371,13 +376,19 @@
<a title="RDF dataset">RDF datasets</a> support this requirement.</p>
<p>An <a>RDF dataset</a> is a collection of
- <a title="RDF graph">RDF graphs</a>. All but one are
- <a title="named graph">named graphs</a> associated with an <a>IRI</a>.
- The last one is the unnamed <a>default graph</a>, and is often used
- to hold <a title="RDF triple">triples</a> that involve the graph names.</p>
+ <a title="RDF graph">RDF graphs</a>. All but one of these graphs have
+ an associated <a>IRI</a>. They are called
+ <a title="named graph">named graphs</a>, and the IRI is called the
+ <a>graph name</a>.
+ The remaining graph does not have an associated IRI, and is called
+ the <a>default graph</a> of the RDF dataset.</p>
- <p>A common use of <a title="RDF dataset">RDF datasets</a> is to hold
- snapshots of multiple <a title="RDF source">RDF sources</a>.</p>
+ <p>There are many possible uses for <a title="RDF dataset">RDF datasets</a>.
+ One such use is to hold snapshots of multiple
+ <a title="RDF source">RDF sources</a>. It is common to have the
+ <a>default graph</a> contain <a title="RDF triple">triples</a>
+ that involve the <a title="graph name">graph names</a>
+ of the other graphs in the dataset.</p>
</section>
@@ -409,16 +420,16 @@
This treatment of RDF graphs as logical expressions is
normatively defined in the
<a href="http://www.w3.org/TR/rdf-mt/">RDF Semantics</a>
- specification [[RDF-MT]], using the formalism of Model Theory.
+ specification [[RDF-MT]], using a model-theoretic semantics.
It yields various relationships between RDF graphs:</p>
<dl>
<dt><dfn>Entailment</dfn></dt>
- <dd>An <a>RDF graph</a> <em>A</em> entail another RDF graph <em>B</em>
- if every possible arrangement of things in the world
- that makes <em>A</em> true also makes <em>B</em> true.
- If the truth of <em>A</em> is presumed or demonstrated,
- then the truth of <em>B</em> can be inferred.</dd>
+ <dd>An <a>RDF graph</a> <em>A</em> entails another RDF graph <em>B</em>
+ if every possible arrangement of the world
+ that makes <em>A</em> true also makes <em>B</em> true. When <em>A</em>
+ entails <em>B</em>, if the truth of <em>A</em> is presumed or demonstrated
+ then the truth of <em>B</em> is established.</dd>
<dt><dfn>Equivalence</dfn></dt>
<dd>Two <a title="RDF graph">RDF graphs</a> <em>A</em> and <em>B</em>
@@ -433,15 +444,16 @@
of the world that would make the expression true.</dd>
</dl>
- <p>What <a title="RDF graph">graphs</a> exactly are considered
- to have these relationships is specified by an
- <dfn>entailment regime</dfn> [[RDF-MT]] combined with a
- <a>datatype map</a>. RDF itself recognizes only some basic conditions.
- Other specifications, such as
+ <p>An <dfn>entailment regime</dfn> [[RDF-MT]] is a specification that
+ defines precise conditions that make these relationships hold.
+ RDF itself recognizes only some basic cases of entailment, equivalence
+ and inconsistency. Other specifications, such as
<a href="http://www.w3.org/TR/rdf-schema/">RDF Schema</a> [[RDF-SCHEMA]]
and <a href="http://www.w3.org/TR/owl2-overview/">OWL 2</a>
[[OWL2-OVERVIEW]], add more powerful entailment regimes,
- as do some domain-specific <a title="vocabulary">vocabularies</a>.</p>
+ as do some domain-specific <a title="RDF vocabulary">vocabularies</a>.
+ Some entailment regimes are defined with respect to a
+ <a>datatype map</a>.</p>
<p>This specification does not constrain how implementations
use the logical relationships defined by
@@ -463,15 +475,14 @@
RDF documents enable the exchange of RDF graphs and RDF datasets
between systems.</p>
- <p>A <a title="concrete RDF syntax">concrete RDF syntaxes<a> may offer
+ <p>A <a>concrete RDF syntax<a> may offer
many different ways to encode the same <a>RDF graph</a> or
<a>RDF dataset</a>, for example through the use of
<a title="namespace prefix">namespace prefixes</a>,
relative IRIs, <a title="blank node identifier">blank node identifiers</a>,
- and different ordering of statmenets. While these aspects can have great
+ and different ordering of statements. While these aspects can have great
effect on the convenience of working with the <a>RDF document</a>,
- they have no effect on its semantics, which lies exclusively in the
- encoded graph or dataset.</p>
+ they are not significant for its meaning.</p>
</section>
@@ -581,7 +592,7 @@
Interoperability problems can be avoided by minting
only IRIs that are normalized according to
<a href="http://tools.ietf.org/html/rfc3987#section-5">Section 5</a>
- of [[!RFC3987]]. Non-normalized forms that should be avoided
+ of [[!RFC3987]]. Non-normalized forms that are best avoided
include:</p>
<ul>
@@ -618,9 +629,9 @@
elements:</p>
<ul>
- <li>a <dfn>lexical form</dfn> being a Unicode [[!UNICODE]] string,
+ <li>a <dfn>lexical form</dfn>, being a Unicode [[!UNICODE]] string,
which SHOULD be in Normal Form C [[!NFC]],</li>
- <li>a <dfn>datatype IRI</dfn> being an <a>IRI</a> that determines
+ <li>a <dfn>datatype IRI</dfn>, being an <a>IRI</a> that determines
how the lexical form maps to a <a>literal value</a>.</li>
</ul>
@@ -702,11 +713,11 @@
<a title="minting">mint</a> a new, globally
unique IRI (a <dfn>Skolem IRI</dfn>) for each blank node so replaced.</p>
- <p>This transformation does not change the meaning of an RDF graph,
- provided that the Skolem IRIs do not occur anywhere else.
+ <p>This transformation does not appreciably change the meaning of an
+ RDF graph, provided that the Skolem IRIs do not occur anywhere else.
It does however permit the possibility of other graphs
- subsequently using the IRI to also refer to the same entity,
- which was not possible when the node was blank.</p>
+ subsequently using the Skolem IRIs, which is not possible
+ for blank nodes.</p>
<p>Systems may wish to mint Skolem IRIs in such a way that they can
recognize the IRIs as having been introduced solely to replace a blank
@@ -752,8 +763,7 @@
<var>G'</var></li>
</ol>
- <p>See also: <a>IRI equality</a>, <a>literal equality</a>,
- <a>blank node equality</a>.</p>
+ <p>See also: <a>IRI equality</a>, <a>literal equality</a>.</p>
<p>With this definition, <var>M</var> shows how each blank node
in <var>G</var> can be replaced with
@@ -768,7 +778,7 @@
<h2>RDF Datasets</h2>
<p>An <dfn>RDF Dataset</dfn> is a collection of
- <a title="RDF graph">RDF graphs</a> and comprises:</p>
+ <a title="RDF graph">RDF graphs</a>, and comprises:</p>
<ul>
<li>Exactly one <dfn>default graph</dfn>, being an <a>RDF graph</a>.
@@ -792,8 +802,8 @@
<p>Some <a>RDF dataset</a>
implementations do not track empty <a title="named graph">named graphs</a>.
- Therefore, to maximize interoperability, applications should avoid
- ascribing importance to the presence of empty named graphs.</p>
+ Applications can avoid interoperability issues by not
+ ascribing importance to the presence or absence of empty named graphs.</p>
</div>
<p class="issue">Should RDF Concepts define any operations on RDF datasets,
@@ -807,11 +817,12 @@
<h2>Datatypes</h2>
<p>Datatypes are used with RDF <a title="literal">literals</a>
- to represent values such as string, numbers and dates.
+ to represent values such as strings, numbers and dates.
The datatype abstraction used in RDF is compatible with XML Schema
[[!XMLSCHEMA11-2]]. Any datatype definition that conforms
to this abstraction MAY be used in RDF, even if not defined
- in terms of XML Schema. RDF re-uses the XML Schema built-in datatypes,
+ in terms of XML Schema. RDF re-uses many of the XML Schema
+ built-in datatypes,
and provides two additional built-in datatypes,
<code><a>rdf:HTML</a></code> and <code><a>rdf:XMLLiteral</a></code>.
The list of datatypes supported by an implementation is determined
@@ -1010,12 +1021,14 @@
<dt>The lexical-to-value mapping</dt>
<dd>
+ <p>Each member of the lexical space is associated with the result
+ of applying the following algorithm:</p>
<ul>
<li>Let <code>domnodes</code> be the list of
<a href="http://www.w3.org/TR/dom/#node">DOM nodes</a> [[!DOM4]]
that result from applying the
<a href="http://www.w3.org/TR/html5/the-end.html#parsing-html-fragments">HTML fragment parsing algorithm</a> [[!HTML5]]
- to the literal's <a>lexical form</a>, without a context element.</li>
+ to the input string, without a context element.</li>
<li>Let <code>domfrag</code> be a DOM
<a href="http://www.w3.org/TR/dom/#interface-documentfragment"><code>DocumentFragment</code></a>
[[!DOM4]] whose <code>childNodes</code> attribute is equal to
@@ -1074,11 +1087,13 @@
<dt id="XMLLiteral-mapping">The lexical-to-value mapping</a></dt>
- <dd><ul>
+ <dd>
+ <p>Each member of the lexical space is associated with the result
+ of applying the following algorithm:</p>
+ <ul>
<li>Let <code>domfrag</code> be a DOM
<a href="http://www.w3.org/TR/dom/#interface-documentfragment"><code>DocumentFragment</code></a>
- node [[!DOM4]] corresponding to the literal's
- <a>lexical form</a></li>
+ node [[!DOM4]] corresponding to the input string</li>
<li>Return <code>domfrag.<a href="http://www.w3.org/TR/dom/#dom-node-normalize">normalize</a>()</code></li>
</ul></dd>
@@ -1109,9 +1124,9 @@
<p>A <dfn>datatype map</dfn> is an implementation-defined set of
<<a>IRI</a>, <a>datatype</a>> pairs such that no
- IRI appears twice in the set and the IRI denotes the datatype.
- It can be seen as a function from IRIs
- to datatypes.</p>
+ IRI appears twice in the set.
+ It can be seen as a function from IRIs to datatypes,
+ where the IRIs denote the datatypes.</p>
<p>If a <a>datatype map</a> contains the IRI
<code>http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral</code>,
@@ -1129,7 +1144,7 @@
<a title="RDF-compatible XSD types">RDF-compatible XSD type</a>
named <code>xsd:<em>xxx</em></code>.<p>
- <p>Other specifications that
+ <p>Other specifications
MAY impose additional constraints on the <a>datatype map</a>,
for example, require support for certain datatypes.</p>
@@ -1194,7 +1209,7 @@
<p>RDF uses <a title="IRI">IRIs</a>, which may include
<dfn>fragment identifiers</dfn>, as resource identifiers.
- The semantics of fragment identifiers are
+ The semantics of fragment identifiers is
<a href="http://tools.ietf.org/html/rfc3986#section-3.5">defined in
RFC 3986</a> [[RFC3986]]: They identify a secondary resource
that is usually a part of, view of, defined in, or described in