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+
+<body id="respecDocument" role="document" class="h-entry"><div id="respecHeader" role="contentinfo" class="head">
+ <p>
+
+ <a href="http://www.w3.org/"><img src="https://www.w3.org/Icons/w3c_home" alt="W3C" height="48" width="72"></a>
+
+ </p>
+ <h1 class="title p-name" id="title" property="dcterms:title">RDF 1.1 Primer</h1>
+
+ <h2 id="w3c-working-group-note-24-june-2014" property="dcterms:issued" datatype="xsd:dateTime" content="2014-06-23T23:00:00.000Z"><abbr title="World Wide Web Consortium">W3C</abbr> Working Group Note <time class="dt-published" datetime="2014-06-24">24 June 2014</time></h2>
+ <dl>
+
+ <dt>This version:</dt>
+ <dd><a class="u-url" href="http://www.w3.org/TR/2014/NOTE-rdf11-primer-20140624/">http://www.w3.org/TR/2014/NOTE-rdf11-primer-20140624/</a></dd>
+ <dt>Latest published version:</dt>
+ <dd><a href="http://www.w3.org/TR/rdf11-primer/">http://www.w3.org/TR/rdf11-primer/</a></dd>
+
+
+ <dt>Latest editor's draft:</dt>
+ <dd><a href="https://dvcs.w3.org/hg/rdf/raw-file/default/rdf-primer/index.html">https://dvcs.w3.org/hg/rdf/raw-file/default/rdf-primer/index.html</a></dd>
+
+
+
+
+
+
+
+
+ <dt>Latest Recommendation:</dt>
+ <dd><a href="http://www.w3.org/TR/rdf-primer">http://www.w3.org/TR/rdf-primer</a></dd>
+
+
+ <dt>Editors:</dt>
+ <dd class="p-author h-card vcard" rel="bibo:editor" inlist=""><span typeof="foaf:Person"><a class="u-url url p-name fn" rel="foaf:homepage" property="foaf:name" content="Guus Schreiber" href="http://www.cs.vu.nl/~guus/">Guus Schreiber</a>, <a rel="foaf:workplaceHomepage" class="p-org org h-org h-card" href="http://www.vu.nl/">VU University Amsterdam</a></span>
+</dd>
+<dd class="p-author h-card vcard" rel="bibo:editor" inlist=""><span typeof="foaf:Person"><a class="u-url url p-name fn" rel="foaf:homepage" property="foaf:name" content="Yves Raimond" href="http://raimond.me.uk/">Yves Raimond</a>, <a rel="foaf:workplaceHomepage" class="p-org org h-org h-card" href="http://www.bbc.co.uk">BBC</a></span>
+</dd>
+
+
+
+
+
+ <dt>Previous Editors:</dt>
+
+
+
+ <dd>
+
+ Frank Manola
+
+ </dd>
+
+
+
+ <dd>
+
+ Eric Miller
+
+ </dd>
+
+
+
+ <dd>
+
+ Brian McBride
+
+ </dd>
+
+
+
+
+
+
+ </dl>
+
+ <p>
+ Please check the <a href="http://www.w3.org/2014/rdf1.1-errata"><strong>errata</strong></a> for any errors or issues
+ reported since publication.
+ </p>
+
+
+ <p>
+
+ This document is also available in this non-normative format:
+
+ <a rel="alternate" href="http://www.asahi-net.or.jp/~ax2s-kmtn/internet/rdf/NOTE-rdf11-primer-20140225.html">Japanese translation</a>
+ </p>
+
+
+
+
+ <p class="copyright">
+ <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> ©
+ 2003-2014
+
+ <a href="http://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup>
+ (<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>,
+ <a href="http://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>,
+ <a href="http://www.keio.ac.jp/">Keio</a>, <a href="http://ev.buaa.edu.cn/">Beihang</a>),
+
+ All Rights Reserved.
+
+ <abbr title="World Wide Web Consortium">W3C</abbr> <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
+ <a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and
+
+ <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document use</a>
+
+ rules apply.
+ </p>
+
+
+ <hr>
+</div>
+
+ <section rel="bibo:Chapter" resource="#abstract" typeof="bibo:Chapter" datatype="" property="dcterms:abstract" class="introductory" id="abstract"><h2 id="h2_abstract" role="heading" aria-level="1">Abstract</h2>
+ <p>This primer is designed to provide the reader with the basic
+ knowledge required to effectively use RDF. It introduces the basic
+ concepts of RDF and shows concrete examples of the use of RDF.
+ Secs. 3-5 can be used as a minimalist introduction into the key
+ elements of RDF. Changes between RDF 1.1
+ and RDF 1.0 (2004 version) are summarized in a separate document: "What's New in RDF
+ 1.1" [<cite><a href="#bib-RDF11-NEW" class="bibref">RDF11-NEW</a></cite>].</p>
+ </section><section rel="bibo:Chapter" resource="#sotd" typeof="bibo:Chapter" id="sotd" class="introductory"><h2 id="h2_sotd" role="heading" aria-level="1">Status of This Document</h2>
+
+
+
+ <p>
+ <em>This section describes the status of this document at the time of its publication.
+ Other documents may supersede this document. A list of current <abbr title="World Wide Web Consortium">W3C</abbr> publications and the
+ latest revision of this technical report can be found in the <a href="http://www.w3.org/TR/"><abbr title="World Wide Web Consortium">W3C</abbr> technical reports index</a> at
+ http://www.w3.org/TR/.</em>
+ </p>
+
+ <p>This document is part of the RDF 1.1 document suite. It is an
+ informative note on the key concepts of RDF. For a normative
+ specification of RDF 1.1 the reader is referred to the RDF
+ 1.1. Concepts and Abstract Syntax document [<cite><a href="#bib-RDF11-CONCEPTS" class="bibref">RDF11-CONCEPTS</a></cite>].</p>
+
+ <p>
+ This document was published by the <a href="http://www.w3.org/2011/rdf-wg/">RDF Working Group</a> as a Working Group Note.
+
+
+ If you wish to make comments regarding this document, please send them to
+ <a href="mailto:public-rdf-comments@w3.org">public-rdf-comments@w3.org</a>
+ (<a href="mailto:public-rdf-comments-request@w3.org?subject=subscribe">subscribe</a>,
+ <a href="http://lists.w3.org/Archives/Public/public-rdf-comments/">archives</a>).
+
+
+
+
+ All comments are welcome.
+
+ </p>
+
+
+ <p>
+ Publication as a Working Group Note does not imply endorsement by the <abbr title="World Wide Web Consortium">W3C</abbr>
+ Membership. This is a draft document and may be updated, replaced or obsoleted by other
+ documents at any time. It is inappropriate to cite this document as other than work in
+ progress.
+ </p>
+
+
+
+ <p>
+
+ This document was produced by a group operating under the
+ <a id="sotd_patent" about="" rel="w3p:patentRules" href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 <abbr title="World Wide Web Consortium">W3C</abbr> Patent
+ Policy</a>.
+
+
+
+
+ <abbr title="World Wide Web Consortium">W3C</abbr> maintains a <a href="http://www.w3.org/2004/01/pp-impl/46168/status" rel="disclosure">public list of any patent
+ disclosures</a>
+
+ made in connection with the deliverables of the group; that page also includes
+ instructions for disclosing a patent. An individual who has actual knowledge of a patent
+ which the individual believes contains
+ <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
+ Claim(s)</a> must disclose the information in accordance with
+ <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
+ 6 of the <abbr title="World Wide Web Consortium">W3C</abbr> Patent Policy</a>.
+
+
+ </p>
+
+
+
+
+</section><section id="toc"><h2 id="h2_toc" role="heading" aria-level="1" class="introductory">Table of Contents</h2><ul id="respecContents" role="directory" class="toc"><li class="tocline"><a class="tocxref" href="#section-Introduction"><span class="secno">1. </span>Introduction</a></li><li class="tocline"><a class="tocxref" href="#section-use-cases"><span class="secno">2. </span>Why Use RDF?</a></li><li class="tocline"><a class="tocxref" href="#section-data-model"><span class="secno">3. </span>RDF Data Model</a><ul class="toc"><li class="tocline"><a class="tocxref" href="#section-triple"><span class="secno">3.1 </span>Triples</a></li><li class="tocline"><a class="tocxref" href="#section-IRI"><span class="secno">3.2 </span>IRIs</a></li><li class="tocline"><a class="tocxref" href="#section-literal"><span class="secno">3.3 </span>Literals</a></li><li class="tocline"><a class="tocxref" href="#section-blank-node"><span class="secno">3.4 </span>Blank nodes</a></li><li class="tocline"><a class="tocxref" href="#section-multiple-graphs"><span class="secno">3.5 </span>Multiple graphs</a></li></ul></li><li class="tocline"><a class="tocxref" href="#section-vocabulary"><span class="secno">4. </span>RDF Vocabularies</a></li><li class="tocline"><a class="tocxref" href="#section-graph-syntax"><span class="secno">5. </span>Writing RDF graphs</a><ul class="toc"><li class="tocline"><a class="tocxref" href="#section-turtle-family"><span class="secno">5.1 </span>Turtle family of RDF languages</a><ul class="toc"><li class="tocline"><a class="tocxref" href="#section-n-triples"><span class="secno">5.1.1 </span>N-Triples</a></li><li class="tocline"><a class="tocxref" href="#section-turtle"><span class="secno">5.1.2 </span>Turtle</a></li><li class="tocline"><a class="tocxref" href="#section-trig"><span class="secno">5.1.3 </span>TriG</a></li><li class="tocline"><a class="tocxref" href="#section-n-quads"><span class="secno">5.1.4 </span>N-Quads</a></li></ul></li><li class="tocline"><a class="tocxref" href="#section-json-ld"><span class="secno">5.2 </span>JSON-LD</a></li><li class="tocline"><a class="tocxref" href="#section-rdfa"><span class="secno">5.3 </span>RDFa</a></li><li class="tocline"><a class="tocxref" href="#section-rdfxml"><span class="secno">5.4 </span>RDF/XML</a></li></ul></li><li class="tocline"><a class="tocxref" href="#section-semantics"><span class="secno">6. </span>Semantics of RDF Graphs</a></li><li class="tocline"><a class="tocxref" href="#section-data"><span class="secno">7. </span>RDF Data</a></li><li class="tocline"><a class="tocxref" href="#section-conclusion"><span class="secno">8. </span>More Information</a></li><li class="tocline"><a class="tocxref" href="#section-Acknowledgments"><span class="secno">A. </span>Acknowledgments</a></li><li class="tocline"><a class="tocxref" href="#section-Changes"><span class="secno">B. </span>Changes since the previous publication</a></li><li class="tocline"><a class="tocxref" href="#references"><span class="secno">C. </span>References</a><ul class="toc"><li class="tocline"><a class="tocxref" href="#informative-references"><span class="secno">C.1 </span>Informative references</a></li></ul></li></ul></section>
+
+
+
+<section rel="bibo:Chapter" resource="#section-Introduction" typeof="bibo:Chapter" id="section-Introduction">
+ <!--OddPage--><h2 id="h2_section-Introduction" role="heading" aria-level="1"><span class="secno">1. </span>Introduction</h2>
+
+ <p>The Resource Description Framework (RDF) is a framework for
+ expressing information about
+ <a href="http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/#resources-and-statements">
+ resources</a>.
+ Resources
+ can be anything, including documents, people, physical objects, and abstract
+ concepts.</p>
+
+ <p>RDF is intended for situations in which information on the Web needs to
+ be processed by applications, rather than being only displayed to
+ people. RDF provides a common framework for expressing this
+ information so it can be exchanged between applications without
+ loss of meaning. Since it is a common framework, application
+ designers can leverage the availability of common RDF parsers and
+ processing tools. The ability to exchange information between
+ different applications means that the information may be made
+ available to applications other than those for which it was
+ originally created. </p>
+
+ <p>In particular RDF can be used to publish and interlink data on the Web.
+ For example, retrieving <code>http://www.example.org/bob#me</code>
+ could provide data about Bob, including the fact that he
+ knows Alice, as identified by her IRI (an IRI is an "International
+ Resource Identifier"; see <a href="#section-IRI">Sec. 3.2</a> for details).
+ Retrieving Alice's IRI could then provide more data about her, including links
+ to other datasets for her friends, interests, etc. A person or
+ an automated process can then follow such links and aggregate data about these
+ various things. Such uses of RDF are often
+ qualified as Linked Data [<cite><a href="#bib-LINKED-DATA" class="bibref">LINKED-DATA</a></cite>]. </p>
+
+ <p>This document is not normative and does not give a complete
+ account of RDF 1.1. Normative
+ specifications of RDF can be found in the following documents: </p>
+ <ul>
+ <li>A document describing the basic concepts underlying RDF, as
+ well as abstract syntax ("RDF Concepts and Abstract Syntax")
+ [<cite><a href="#bib-RDF11-CONCEPTS" class="bibref">RDF11-CONCEPTS</a></cite>]</li>
+ <li>A document describing the formal model-theoretic semantics
+ of RDF ("RDF Semantics") [<cite><a href="#bib-RDF11-MT" class="bibref">RDF11-MT</a></cite>]</li>
+ <li>Specifications of serialization formats for RDF:
+ <ul>
+ <li>Turtle [<cite><a href="#bib-TURTLE" class="bibref">TURTLE</a></cite>] and TriG [<cite><a href="#bib-TRIG" class="bibref">TRIG</a></cite>]</li>
+ <li>JSON-LD [<cite><a href="#bib-JSON-LD" class="bibref">JSON-LD</a></cite>] (JSON based)</li>
+ <li>RDFa [<cite><a href="#bib-RDFA-PRIMER" class="bibref">RDFA-PRIMER</a></cite>] (for HTML embedding)</li>
+ <li>N-Triples [<cite><a href="#bib-N-TRIPLES" class="bibref">N-TRIPLES</a></cite>] and N-Quads [<cite><a href="#bib-N-QUADS" class="bibref">N-QUADS</a></cite>]
+ (line-based exchange formats)</li>
+ <li>RDF/XML [<cite><a href="#bib-RDF11-XML" class="bibref">RDF11-XML</a></cite>] (the original 2004 syntax, updated
+ for RDF 1.1)</li>
+ </ul></li>
+ <li>A document describing RDF Schema [<cite><a href="#bib-RDF11-SCHEMA" class="bibref">RDF11-SCHEMA</a></cite>], which
+ provides a data-modeling vocabulary for RDF data. </li>
+ </ul>
+
+</section>
+
+<section rel="bibo:Chapter" resource="#section-use-cases" typeof="bibo:Chapter" id="section-use-cases">
+ <!--OddPage--><h2 id="h2_section-use-cases" role="heading" aria-level="1"><span class="secno">2. </span>Why Use RDF?</h2>
+
+ <p>The following illustrates various different uses of RDF, aimed
+ at different communities of practice.</p>
+
+ <ul>
+ <li>Adding machine-readable information to Web pages using, for example,
+ the popular <a href="http://schema.org">schema.org</a>
+ vocabulary, enabling them to be displayed
+ in an enhanced format on search engines or to be processed automatically
+ by third-party applications.</li>
+ <li>Enriching a dataset by linking it to third-party
+ datasets. For example, a dataset about
+ paintings could be enriched by linking them to the corresponding
+ artists in <a href="http://www.wikidata.org">Wikidata</a>,
+ therefore giving access to a wide range of information about
+ them and related resources.</li>
+ <li>Interlinking API feeds, making sure that clients can easily
+ discover how to access more information.</li>
+ <li>Using the datasets currently published as Linked Data
+ [<cite><a href="#bib-LINKED-DATA" class="bibref">LINKED-DATA</a></cite>], for example
+ building aggregations of data around specific topics.</li>
+ <li>Building distributed social networks by interlinking RDF
+ descriptions of people
+ across multiple Web sites.</li>
+ <li>Providing a standards-compliant way for exchanging data
+ between databases.</li>
+ <li>Interlinking various datasets within an organisation,
+ enabling cross-dataset queries to
+ be performed using SPARQL [<cite><a href="#bib-SPARQL11-OVERVIEW" class="bibref">SPARQL11-OVERVIEW</a></cite>].</li>
+ </ul>
+
+</section>
+
+<section rel="bibo:Chapter" resource="#section-data-model" typeof="bibo:Chapter" id="section-data-model">
+
+ <!--OddPage--><h2 id="h2_section-data-model" role="heading" aria-level="1"><span class="secno">3. </span>RDF Data Model</h2>
+
+ <section rel="bibo:Chapter" resource="#section-triple" typeof="bibo:Chapter" id="section-triple">
+
+ <h3 id="h3_section-triple" role="heading" aria-level="2"><span class="secno">3.1 </span>Triples</h3>
+
+ <p>RDF allows us to make statements about resources.
+ The format of these statements is simple. A statement always
+ has the following structure:</p><p>
+ </p><pre> <subject> <predicate> <object>
+ </pre>
+
+ <!--
+ <p>The <strong>subject</strong> represents the resource we like to
+ make a statement about. The <strong>predicate</strong> represents
+ a property of the subject. The
+ <strong>object</strong> represents a value of the property
+ for this subject. Because RDF statements consist of three elements they are called
+ <strong>triples</strong>.</p>
+ -->
+
+ <p>An RDF statement expresses a relationship between two resources.
+ The <strong>subject</strong> and the <strong>object</strong>
+ represent the two resources being
+ related; the <strong>predicate</strong> represents the nature of their
+ relationship. The relationship is phrased in a directional way
+ (from subject to object) and is called in RDF a
+ <strong>property</strong>. Because RDF statements consist of
+ three elements they are called <strong>triples</strong>.
+ </p>
+
+ <p>Here are examples of RDF triples (informally expressed in pseudocode):</p>
+
+ <div class="example"><div class="example-title"><span>Example 1</span>: Sample triples (informal)</div><pre class="example" id="example1"><Bob> <is a> <person>.
+<Bob> <is a friend of> <Alice>.
+<Bob> <is born on> <the 4th of July 1990>.
+<Bob> <is interested in> <the Mona Lisa>.
+<the Mona Lisa> <was created by> <Leonardo da Vinci>.
+<the video 'La Joconde à Washington'> <is about> <the Mona Lisa></pre></div>
+
+ <p>The same resource is often referenced in multiple triples. In the example above,
+ Bob is the subject of four triples, and the Mona Lisa is the subject of
+ one and the object of two triples. This ability to have the same resource be
+ in the subject position of one triple and the object position of another
+ makes it possible to find connections between triples, which is an
+ important part of RDF's power.</p>
+
+ <p>We can visualize triples as a connected
+ <strong>graph</strong>. Graphs consists
+ of nodes and arcs. The subjects and
+ objects of the triples make up the nodes in the graph; the
+ predicates form the arcs. <a class="fig-ref" href="#fig1">Fig. 1</a>
+ shows the graph resulting from the sample triples.</p>
+
+ <figure id="fig1">
+ <img class="graph" src="example-graph.jpg" alt="Informal graphs of the sample triples">
+ <figcaption>Fig. <span class="figno">1</span> <span class="fig-title">Informal graph of the sample triples</span></figcaption>
+ </figure>
+
+ <p>Once you have a graph like this you can use SPARQL [<cite><a href="#bib-SPARQL11-OVERVIEW" class="bibref">SPARQL11-OVERVIEW</a></cite>] to
+ query for e.g. people interested in paintings by Leonardo da
+ Vinci.</p>
+
+ <p>The RDF Data Model is described in this section
+ in the form of an "abstract syntax", i.e. a data model that is independent of a
+ particular concrete syntax (the syntax used to represent triples stored in
+ text files). Different concrete syntaxes may
+ produce exactly the same graph from the perspective of the
+ abstract syntax. The semantics of RDF graphs [<cite><a href="#bib-RDF11-MT" class="bibref">RDF11-MT</a></cite>] are defined in
+ terms of this abstract syntax. Concrete RDF syntax is introduced
+ later in <a href="#section-graph-syntax">Sec. 5</a>.</p>
+
+ <p>In the next three subsections we discuss the three types of RDF data
+ that occur in triples: IRIs, literals and blank nodes. </p>
+
+ </section>
+
+ <section rel="bibo:Chapter" resource="#section-IRI" typeof="bibo:Chapter" id="section-IRI">
+
+ <h3 id="h3_section-IRI" role="heading" aria-level="2"><span class="secno">3.2 </span>IRIs</h3>
+
+
+ <p>The abbreviation IRI is short for "International Resource
+ Identifier". An <a href="http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/#section-IRIs">IRI</a>
+ identifies a resource. The URLs (Uniform Resource Locators) that
+ people use as Web addresses are one form of IRI. Other forms of IRI
+ provide an identifier for a resource without implying its location
+ or how to access it. The notion of IRI is a
+ generalization of URI (Uniform Resource Identifier), allowing
+ non-ASCII characters to be used in the IRI character string. IRIs are specified
+ in RFC 3987 [<cite><a href="#bib-RFC3987" class="bibref">RFC3987</a></cite>].
+
+ </p><p>IRIs can appear in <strong>all three positions</strong> of a triple. </p>
+
+ <p>As mentioned, IRIs are used to identify resources such as documents,
+ people, physical objects, and abstract concepts.
+ For example, the IRI for Leonardo da Vinci in <a href="http://dbpedia.org">DBpedia</a> is:</p>
+
+ <div class="example"><a href="http://dbpedia.org/resource/Leonardo_da_Vinci">http://dbpedia.org/resource/Leonardo_da_Vinci</a></div>
+
+ <p>The IRI for an <a href="http://www.ina.fr">INA</a> video about the Mona Lisa entitled 'La Joconde à Washington' in <a href="http://www.europeana.eu">Europeana</a> is:</p>
+
+ <div class="example"><a href="http://data.europeana.eu/item/04802/243FA8618938F4117025F17A8B813C5F9AA4D619">http://data.europeana.eu/item/04802/243FA8618938F4117025F17A8B813C5F9AA4D619</a></div>
+
+ <p>IRIs are global identifiers, so other people can re-use this
+ IRI to identify the same thing. For example, the following IRI is
+ used by many people as an RDF property to state an acquaintance
+ relationship between people:</p>
+
+ <div class="example"><a href="http://xmlns.com/foaf/0.1/knows">http://xmlns.com/foaf/0.1/knows</a></div>
+
+ <p>RDF is agnostic about what the IRI represents. However,
+ IRIs may be given meaning by particular vocabularies or
+ conventions. For example, <a href="http://wiki.dbpedia.org/Datasets#h338-3">DBpedia</a> uses IRIs of the form
+ <code>http://dbpedia.org/resource/Name</code> to denote the thing
+ described by the corresponding Wikipedia article.</p>
+
+ </section>
+
+ <section rel="bibo:Chapter" resource="#section-literal" typeof="bibo:Chapter" id="section-literal">
+
+ <h3 id="h3_section-literal" role="heading" aria-level="2"><span class="secno">3.3 </span>Literals</h3>
+
+ <p>
+ <a href="http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/#section-Graph-Literal">Literals</a>
+ are basic values that are not IRIs. Examples of literals include
+ strings such as "La Joconde", dates such as "the 4th of July, 1990"
+ and numbers such as "3.14159".
+ Literals are associated with a <a href="http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/#section-Datatypes">datatype</a>
+ enabling such values to be parsed and interpreted correctly.
+ String literals can optionally be associated with a <a href="http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/#section-Graph-Literal">language
+ tag</a>. For example, "Léonard de Vinci" could
+ be associated with the "fr" language tag and "李奥纳多·达·文西"
+ with the "zh" language tag.</p>
+
+ <!--
+ <p class="note">The 2004 version of RDF contained the notion of a
+ "plain literal" with no datatype. This feature has been removed, as the
+ distinction between "plain" literals and literals with datatype
+ <code>string</code> was confusing. RDF languages such as Turtle allow
+ writing of literals without an explicit datatype and treat this
+ as syntactic sugar for a <code>string</code>
+ datatype. The special datatype
+ <code>rdf:langString</code> is assigned to language-tagged
+ literals.</p>
+ -->
+
+ <p>Literals may only appear in the <strong>object position</strong> of a triple.</p>
+
+ <p>The RDF Concepts document provides a (non-exhaustive)
+ <a href="http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/#section-Datatypes">list
+ of datatypes</a>. This includes many datatypes defined by XML
+ Schema, such as string, boolean, integer, decimal and date. </p>
+
+ </section>
+
+ <section rel="bibo:Chapter" resource="#section-blank-node" typeof="bibo:Chapter" id="section-blank-node">
+
+ <h3 id="h3_section-blank-node" role="heading" aria-level="2"><span class="secno">3.4 </span>Blank nodes</h3>
+
+ <p>IRIs and literals together provide the basic material for
+ writing down RDF statements. In addition, it is sometimes handy
+ to be able to talk about resources without bothering to use a global
+ identifier. For example, we might want to state that the Mona
+ Lisa painting has in its background an unidentified tree which
+ we know to be a cypress tree. A resource without a global identifier, such as the
+ painting's cypress tree, can be represented in RDF by a <a href="http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/#section-blank-nodes">blank
+ node</a>. Blank nodes are like simple
+ variables in algebra; they represent some thing without saying
+ what their value is.
+ </p>
+
+ <p>Blank nodes can appear in the <strong>subject and object
+ position</strong> of a triple. They can be used
+ to denote resources without explicitly naming them with an
+ IRI.</p>
+
+ <figure id="fig2">
+ <img class="graph" src="example-blank-node.jpg" alt="Blank node example: cypress tree">
+ <figcaption>Fig. <span class="figno">2</span> <span class="fig-title">Informal blank node example: the background of the Mona Lisa depicts
+ an unnamed resource that belongs to the class of cypress trees.</span></figcaption>
+ </figure>
+
+
+ </section>
+
+ <section rel="bibo:Chapter" resource="#section-multiple-graphs" typeof="bibo:Chapter" id="section-multiple-graphs">
+
+ <h3 id="h3_section-multiple-graphs" role="heading" aria-level="2"><span class="secno">3.5 </span>Multiple graphs</h3>
+
+ <p>RDF provides a mechanism to group RDF statements in multiple
+ graphs and associate such graphs with an IRI . Multiple graphs are a recent extension of the RDF
+ data model. In practice, RDF tool builders and data managers
+ needed a mechanism to talk about subsets of a collection of
+ triples. Multiple graphs were first introduced in the RDF query
+ language SPARQL. The RDF data model was therefore extended with a notion of
+ multiple graphs that is closely aligned with SPARQL.</p>
+
+ <p>Multiple graphs in
+ an RDF document constitute an
+ <a href="http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/#section-dataset">RDF
+ dataset</a>. An RDF dataset may have multiple named graphs and
+ at most one unnamed ("default") graph. </p><p>
+
+ </p><p>For example, the
+ statements in <a href="#example1">Example 1</a>
+ could be grouped in two named
+ graphs. A first graph could be provided by a social networking
+ site and identified by <code>http://example.org/bob</code>:</p>
+
+ <div class="example"><div class="example-title"><span>Example 2</span>: First graph in the sample dataset</div><pre class="example"><Bob> <is a> <person>.
+<Bob> <is a friend of> <Alice>.
+<Bob> <is born on> <the 4th of July 1990>.
+<Bob> <is interested in> <the Mona Lisa>.</pre></div>
+
+ <p>The IRI associated with the graph is
+ called the <a href="http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/#section-dataset">graph
+ name</a>. </p>
+
+ <p>A second graph could be provided by <a href="http://www.wikidata.org/">Wikidata</a>
+ and identified by
+ <code>https://www.wikidata.org/wiki/Special:EntityData/Q12418</code>:</p>
+
+ <div class="example"><div class="example-title"><span>Example 3</span>: Second graph in the sample dataset</div><pre class="example"><Leonardo da Vinci> <is the creator of> <the Mona Lisa>.
+<The video 'La Joconde à Washington'> <is about> <the Mona Lisa></pre></div>
+
+ <p>Below is an example of an unnamed graph. It contains two triples that
+ have the graph name <code><http://example.org/bob></code>
+ as subject. The triples associate publisher and license information with
+ this graph IRI: </p>
+
+ <div class="example"><div class="example-title"><span>Example 4</span>: Unnamed graph in the sample dataset</div><pre class="example"><http://example.org/bob> <is published by> <http://example.org>.
+<http://example.org/bob> <has license> <http://creativecommons.org/licenses/by/3.0/>.</pre></div>
+
+ <p> In this example dataset we assume graph
+ names represent the source of the RDF data held within the
+ corresponding graphs, i.e. by retrieving
+ <code><http://example.org/bob></code> we would get access to the four triples
+ in that graph.</p>
+
+ <div class="note"><div id="h_note_1" role="heading" aria-level="3" class="note-title"><span>Note</span></div><p class="">RDF provides no standard way to convey this semantic
+ assumption (i.e., that graph names represent the source of the
+ RDF data) to other readers of the dataset. Those readers will
+ need to rely on out-of-band knowledge, such as established
+ community practice, to interpret the dataset
+ in the intended way. Possible semantics of datasets are described in a separate note
+ [<cite><a href="#bib-RDF11-DATASETS" class="bibref">RDF11-DATASETS</a></cite>]. </p></div>
+
+ <figure id="fig3">
+ <img class="graph" src="example-multiple-graphs.jpg" alt="Informal graph of the sample dataset">
+ <figcaption>Fig. <span class="figno">3</span> <span class="fig-title">Informal graph of the sample dataset</span></figcaption>
+ </figure>
+
+ <p><a class="fig-ref" href="#fig3">Fig. 3</a> depicts the sample dataset.
+ <a href="#section-trig">Sec. 5.1.3</a> provides an example
+ of concrete syntax for this dataset.</p>
+
+ </section>
+
+</section>
+
+<section rel="bibo:Chapter" resource="#section-vocabulary" typeof="bibo:Chapter" id="section-vocabulary">
+
+ <!--OddPage--><h2 id="h2_section-vocabulary" role="heading" aria-level="1"><span class="secno">4. </span>RDF Vocabularies</h2>
+
+ <p>The RDF data model provides a way to make statements about
+ resources. As we mentioned, this data model does not make any
+ assumptions about what resource IRIs stand for. In practice, RDF
+ is typically used in combination with vocabularies or other
+ conventions that provide semantic information about these
+ resources. </p>
+
+ <p>To support the definition of vocabularies RDF provides
+ the RDF Schema language
+ [<cite><a href="#bib-RDF11-SCHEMA" class="bibref">RDF11-SCHEMA</a></cite>]. This language allows one to define semantic
+ characteristics of
+ RDF data. For example, one can state that the IRI
+ <code>http://www.example.org/friendOf</code> can be used as a property and that the
+ subjects and objects of <code>http://www.example.org/friendOf</code> triples must be
+ resources of class <code>http://www.example.org/Person</code>. </p><p>
+
+ </p><p>RDF Schema uses the notion of <strong>class</strong> to
+ specify categories that can be used to classify resources. The
+ relation between an instance and its class is stated through the
+ <strong>type</strong> property. With RDF Schema one can create hierarchies
+ of classes and sub-classes and of
+ properties and sub-properties. Type restrictions on the subjects
+ and objects of particular triples can be defined through
+ <strong>domain</strong> and <strong>range</strong>
+ restrictions. An example of a domain restriction was given above:
+ subjects of "friendOf" triples should be of class "Person".</p>
+
+ <p>The main modeling
+ constructs provided by RDF Schema are summarized in the table below:</p>
+
+
+<table id="table-rdf-schema">
+ <caption>Table 1: RDF Schema Constructs</caption>
+ <tbody>
+ <tr>
+ <th>Construct</th>
+ <th>Syntactic form</th>
+ <th>Description</th>
+ </tr>
+ <tr>
+ <td><a href="http://www.w3.org/TR/rdf-schema/#ch_classes">Class</a> (a class)</td>
+ <td><strong>C</strong> <code>rdf:type rdfs:Class</code></td>
+ <td><strong>C</strong> (a resource) is an RDF class</td>
+ </tr>
+ <tr>
+ <td><a href="http://www.w3.org/TR/rdf-schema/#ch_property">Property</a> (a class)</td>
+ <td><strong>P</strong> <code>rdf:type rdf:Property</code></td>
+ <td><strong>P</strong> (a resource) is an RDF property</td>
+ </tr>
+ <tr>
+ <td><a href="http://www.w3.org/TR/rdf-schema/#ch_type">type</a> (a property)</td>
+ <td><strong>I</strong> <code>rdf:type</code> <strong>C</strong></td>
+ <td><strong>I</strong> (a resource) is an instance of <strong>C</strong> (a class)</td>
+ </tr>
+ <tr>
+ <td><a href="http://www.w3.org/TR/rdf-schema/#ch_subclassof">subClassOf</a> (a property)</td>
+ <td><strong>C1</strong> <code>rdfs:subClassOf</code> <strong>C2</strong></td>
+ <td><strong>C1</strong> (a class) is a subclass of <strong>C2</strong> (a class)</td>
+ </tr>
+ <tr>
+ <td><a href="http://www.w3.org/TR/rdf-schema/#ch_subpropertyof">subPropertyOf</a> (a property)</td>
+ <td><strong>P1</strong> <code>rdfs:subPropertyOf</code> <strong>P2</strong></td>
+ <td><strong>P1</strong> (a property) is a sub-property of <strong>P2</strong> (a property)</td>
+ </tr>
+ <tr>
+ <td><a href="http://www.w3.org/TR/rdf-schema/#ch_domain">domain</a> (a property)</td>
+ <td><strong>P</strong> <code>rdfs:domain</code> <strong>C</strong></td>
+ <td>domain of <strong>P</strong> (a property) is <strong>C</strong> (a class)</td>
+ </tr>
+ <tr>
+ <td><a href="http://www.w3.org/TR/rdf-schema/#ch_range">range</a> (a property)</td>
+ <td><strong>P</strong> <code>rdfs:range</code> <strong>C</strong></td>
+ <td>range of <strong>P</strong> (a property) is <strong>C</strong> (a class)</td>
+ </tr>
+ </tbody>
+</table>
+
+<div class="note"><div id="h_note_2" role="heading" aria-level="2" class="note-title"><span>Note</span></div><p class="">The syntactic form (second column) is in a prefix
+notation which is discussed in more detail in
+<a href="#section-graph-syntax">Sec. 5</a>.
+The fact that the constructs have two different prefixes
+(<code>rdf:</code> and <code>rdfs:</code>) is a somewhat annoying
+historical artefact, which is preserved for backward
+compatibility.</p></div>
+
+<p>With the help of RDF Schema one can build a model of RDF data. A
+simple informal example:</p>
+
+ <div class="example"><div class="example-title"><span>Example 5</span>: RDF Schema triples (informal)</div><pre class="example" id="rdfs-example"><Person> <<strong>type</strong>> <Class>
+<is a friend of> <<strong>type</strong>> <Property>
+<is a friend of> <<strong>domain</strong>> <Person>
+<is a friend of> <<strong>range</strong>> <Person>
+<is a good friend of> <<strong>subPropertyOf</strong>> <is a friend of></pre></div>
+
+<p>Note that, while <code><is a friend of></code> is a
+property typically used as the predicate of a triple (as it was in
+<a href="#example1">Example 1</a>), properties like this are themselves resources that can be
+described by triples or provide values in the descriptions of other
+resources. In this example, <code><is a friend of></code> is the subject of triples
+that assign type, domain, and range values to it, and it is the object of
+a triple that describes something about the <code><is a good friend of></code>
+property.
+
+</p><p>One of the first RDF vocabularies used worldwide was the
+<a href="http://www.foaf-project.org/">"Friend of a Friend"</a> (FOAF)
+vocabulary for describing social networks. Other examples of RDF
+vocabularies are:</p>
+
+<dl>
+ <dt><a href="http://dublincore.org/documents/dcmi-terms/">Dublin Core</a></dt>
+ <dd>The Dublin Core Metadata Initiative maintains a metadata element
+ set for describing a wide range of resources. The vocabulary provides
+ properties such as "creator", "publisher" and "title".</dd>
+
+ <dt><a href="http://schema.org/">schema.org</a>
+ </dt><dd>Schema.org is a vocabulary developed by a group of major search
+ providers. The idea is that webmasters can use these terms to mark-up
+ Web pages, so that search engines understand what the pages are
+ about.</dd>
+
+ <dt><a href="http://www.w3.org/2004/02/skos/">SKOS</a></dt>
+ <dd>SKOS is a vocabulary for publishing classification schemes
+ such as terminologies and thesauri on the Web. SKOS is since 2009 a <abbr title="World Wide Web Consortium">W3C</abbr>
+ recommendation and is widely used in the library world. The Library of
+ Congress published its Subject Headings as a <a href="http://id.loc.gov/authorities/subjects.html">SKOS
+ vocabulary</a>.</dd>
+</dl>
+
+<p>Vocabularies get their value from reuse: the more vocabulary IRIs
+are reused by others, the more valuable it becomes to use the
+IRIs (the so-called network effect). This means you should prefer
+re-using someone else's IRI instead of inventing a new one. </p>
+
+<p>For a formal specification of the semantics of the RDF Schema
+constructs the reader is referred to
+the RDF Semantics document [<cite><a href="#bib-RDF11-MT" class="bibref">RDF11-MT</a></cite>]. Users interested in more comprehensive
+semantic modeling of RDF data might consider using OWL
+[<cite><a href="#bib-OWL2-OVERVIEW" class="bibref">OWL2-OVERVIEW</a></cite>]. OWL is an RDF vocabulary, so it can be
+used in combination with RDF Schema.</p>
+
+</section>
+
+<section rel="bibo:Chapter" resource="#section-graph-syntax" typeof="bibo:Chapter" id="section-graph-syntax">
+
+ <!--OddPage--><h2 id="h2_section-graph-syntax" role="heading" aria-level="1"><span class="secno">5. </span>Writing RDF graphs</h2>
+
+ <p>A number of different serialization formats exist for writing down RDF
+ graphs. However, different ways of writing down the same graph lead
+ to exactly the same triples, and are thus logically equivalent. </p>
+
+ <p>In this section we briefly introduce, through annotated examples, the following formats:</p>
+<ol>
+ <li>Turtle family of RDF languages
+ (<a href="#section-n-triples">N-Triples</a>,
+ <a href="#section-turtle">Turtle</a>,
+ <a href="#section-trig">TriG</a> and
+ <a href="#section-n-quads">N-Quads</a>);</li>
+ <li><a href="#section-json-ld">JSON-LD</a> (JSON-based RDF syntax);</li>
+ <li><a href="#section-rdfa">RDFa</a> (for HTML and XML embedding);</li>
+ <li><a href="#section-rdfxml">RDF/XML</a> (XML syntax for RDF). </li>
+</ol>
+
+<div class="note"><div id="h_note_3" role="heading" aria-level="2" class="note-title"><span>Note</span></div><p class="">
+Reading tip: Sec. 5.1 (Turtle <em>et al.</em>) discusses all
+basic concepts for serializing RDF. We suggest you
+read the sections on JSON-LD, RDFa and RDF/XML only if you are
+interested in that particular usage of RDF. </p></div>
+
+<section rel="bibo:Chapter" resource="#section-turtle-family" typeof="bibo:Chapter" id="section-turtle-family">
+<h3 id="h3_section-turtle-family" role="heading" aria-level="2"><span class="secno">5.1 </span>Turtle family of RDF languages</h3>
+
+<p>In this subsection we introduce four RDF languages
+which are closely related. We start with N-Triples, as it provides
+basic syntax for writing down RDF triples. The Turtle syntax
+extends this basic syntax with various forms of syntactic sugar to improve
+readability. Subsequently we discuss TriG and N-Quads, which are
+extensions respectively of Turtle and
+N-Triples to encode multiple graphs. Together, these four are
+referred to as the "Turtle family of RDF languages".
+
+</p><section rel="bibo:Chapter" resource="#section-n-triples" typeof="bibo:Chapter" id="section-n-triples">
+<h4 id="h4_section-n-triples" role="heading" aria-level="3"><span class="secno">5.1.1 </span>N-Triples</h4>
+
+<p>N-Triples [<cite><a href="#bib-N-TRIPLES" class="bibref">N-TRIPLES</a></cite>] provides a simple line-based, plain-text way for serializing RDF
+graphs. The informal graph in <a class="fig-ref" href="#fig1">Fig. 1</a> can be represented in N-Triples in the
+following way:</p>
+
+<div class="example"><div class="example-title"><span>Example 6</span>: N-Triples</div><pre class="example" id="n-triples-example"><span class="linenum">01</span> <http://example.org/bob#me> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://xmlns.com/foaf/0.1/Person> .
+<span class="linenum">02</span> <http://example.org/bob#me> <http://xmlns.com/foaf/0.1/knows> <http://example.org/alice#me> .
+<span class="linenum">03</span> <http://example.org/bob#me> <http://schema.org/birthDate> "1990-07-04"^^<http://www.w3.org/2001/XMLSchema#date> .
+<span class="linenum">04</span> <http://example.org/bob#me> <http://xmlns.com/foaf/0.1/topic_interest> <http://www.wikidata.org/entity/Q12418> .
+<span class="linenum">05</span> <http://www.wikidata.org/entity/Q12418> <http://purl.org/dc/terms/title> "Mona Lisa" .
+<span class="linenum">06</span> <http://www.wikidata.org/entity/Q12418> <http://purl.org/dc/terms/creator> <http://dbpedia.org/resource/Leonardo_da_Vinci> .
+<span class="linenum">07</span> <http://data.europeana.eu/item/04802/243FA8618938F4117025F17A8B813C5F9AA4D619> <http://purl.org/dc/terms/subject> <http://www.wikidata.org/entity/Q12418> .</pre></div>
+
+<p>Each line represents a triple. Full IRIs are enclosed in angle brackets
+(<code><></code>). The period at the end of the line signals the
+end of the triple. In line 3 we see an example of a literal, in this case a date. The
+datatype is appended to the literal through a <code>^^</code> delimiter. The date
+representation follows the conventions of the XML Schema datatype
+<a href="http://www.w3.org/TR/xmlschema11-2/#date">date</a>.</p>
+
+<p>Because string literals are so ubiquitous N-Triples allows the user to
+omit the datatype when writing a string literal. Thus, <code>"Mona
+Lisa"</code> in line 5 is equivalent to
+<code>"Mona Lisa"^^xsd:string</code>.
+In case of language-tagged strings the tag
+appears directly after the string, separated by a <code>@</code>
+symbol, e.g. <code>"La Joconde"@fr</code> (the French name of the Mona
+Lisa).</p>
+
+<div class="note"><div id="h_note_4" role="heading" aria-level="4" class="note-title"><span>Note</span></div><p class="">For technical reasons the datatype of language-tagged
+strings is not <code>xsd:string</code> but
+<code>rdf:langString</code>. The
+datatype of language-tagged strings is never specified explicitly.</p></div>
+
+<p>The figure below shows the triples resulting from the example:</p>
+
+ <figure id="fig4">
+ <img style="width: 75%" src="example-graph-iris.jpg" alt="Graph of the sample triples">
+ <figcaption>Fig. <span class="figno">4</span> <span class="fig-title">RDF graph resulting from the N-Triples example</span></figcaption>
+ </figure>
+
+<p>Note that the seven lines in the N-Triples example correspond to the seven
+arcs in the diagram above.</p>
+
+<p>N-Triples is often used for exchanging large amounts of RDF and for
+processing large RDF graphs with line-oriented text processing
+tools. </p>
+
+</section>
+
+<section rel="bibo:Chapter" resource="#section-turtle" typeof="bibo:Chapter" id="section-turtle">
+<h4 id="h4_section-turtle" role="heading" aria-level="3"><span class="secno">5.1.2 </span>Turtle</h4>
+
+<p>Turtle [<cite><a href="#bib-TURTLE" class="bibref">TURTLE</a></cite>] is an <strong>extension of N-Triples</strong>.
+In addition to the basic N-Triples syntax, Turtle
+introduces a number of syntactic shortcuts, such as
+support for namespace prefixes, lists and shorthands for datatyped
+literals. Turtle provides a trade-off between ease of
+writing, ease of parsing and readability. The graph shown in
+<a class="fig-ref" href="#fig4">Fig. 4</a> can be
+represented in Turtle as follows:</p>
+
+<div class="example"><div class="example-title"><span>Example 7</span>: Turtle</div><pre class="example" id="turtle-example"><span class="linenum">01</span> BASE <http://example.org/>
+<span class="linenum">02</span> PREFIX foaf: <http://xmlns.com/foaf/0.1/>
+<span class="linenum">03</span> PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
+<span class="linenum">04</span> PREFIX schema: <http://schema.org/>
+<span class="linenum">05</span> PREFIX dcterms: <http://purl.org/dc/terms/>
+<span class="linenum">06</span> PREFIX wd: <http://www.wikidata.org/entity/>
+<span class="linenum">07</span>
+<span class="linenum">08</span> <bob#me>
+<span class="linenum">09</span> a foaf:Person ;
+<span class="linenum">10</span> foaf:knows <alice#me> ;
+<span class="linenum">11</span> schema:birthDate "1990-07-04"^^xsd:date ;
+<span class="linenum">12</span> foaf:topic_interest wd:Q12418 .
+<span class="linenum">13</span>
+<span class="linenum">14</span> wd:Q12418
+<span class="linenum">15</span> dcterms:title "Mona Lisa" ;
+<span class="linenum">16</span> dcterms:creator <http://dbpedia.org/resource/Leonardo_da_Vinci> .
+<span class="linenum">17</span>
+<span class="linenum">18</span> <http://data.europeana.eu/item/04802/243FA8618938F4117025F17A8B813C5F9AA4D619>
+<span class="linenum">19</span> dcterms:subject wd:Q12418 .</pre></div>
+
+<p>The Turtle example is logically equivalent to the <a href="#n-triples-example">N-Triples</a>
+example. Lines 1-6 contain a number of directives which provide shorthands for
+writing down IRIs. Relative IRIs (such as <code>bob#me</code> on line 8) are
+resolved against a base IRI, specified here in line 1.
+Lines 2-6 define IRI prefixes (such as <code>foaf:</code>), which can
+be used for prefixed names (such as <code>foaf:Person</code>) instead of full IRIs.
+The corresponding IRI is constructed by replacing the prefix with its
+corresponding IRI (in this example <code>foaf:Person</code> stands for
+<code><http://xmlns.com/foaf/0.1/Person></code>).</p>
+
+<p>Lines 8-12 show how Turtle provides a shorthand for a set of
+triples with the same subject. Lines 9-12 specify the predicate-object
+part of triples that have <code><http://example.org/bob#me></code> as
+their subject. The semicolons at the end of lines 9-11 indicate that
+the predicate-object pair that follows it is part of
+a new triple that uses the most recent subject shown in the data — in
+this case <code>bob#me</code>. </p>
+
+<p>Line 9 shows an example of a special kind of syntactic sugar. The triple
+should informally be read as "Bob (is) a Person". The
+<code>a</code> predicate
+is a shorthand for the property <code>rdf:type</code> which models the
+instance relation (see <a href="#table-rdf-schema">Table 1</a>).
+The <code>a</code> shorthand is intended to match the human
+intuition about <code>rdf:type</code>. </p>
+
+<h4 id="representation-of-blank-nodes">Representation of blank nodes</h4>
+
+<p>Below we see two syntactic variants for writing down blank nodes, using the
+earlier cypress tree example.</p>
+
+<div class="example"><div class="example-title"><span>Example 8</span>: Blank node</div><pre class="example">PREFIX lio: <http://purl.org/net/lio#>
+
+<http://dbpedia.org/resource/Mona_Lisa> lio:shows _:x .
+_:x a <http://dbpedia.org/resource/Cypress> .</pre></div>
+
+<p>The term <code>_:x</code> is a blank node. It represents an
+unnamed resource depicted in
+the Mona Lisa painting; the unnamed resource is an instance of the
+<code>Cypress</code> class. The example above provides concrete syntax
+for the informal graph in <a class="fig-ref" href="#fig2">Fig. 2</a>.</p>
+
+<p>Turtle also has an alternative notation for blank nodes, which
+does not require the use of syntax like <code>_:x</code>: </p>
+
+<div class="example"><div class="example-title"><span>Example 9</span>: Blank nodes (alternative notation)</div><pre class="example">@prefix foaf: <http://xmlns.com/foaf/0.1/> .
+
+# Some resource (blank node) is interested in some other resource
+# entitled "Mona Lisa" and created by Leonardo da Vinci.
+
+[] foaf:topic_interest [
+ dcterms:title "Mona Lisa" ;
+ dcterms:creator <http://dbpedia.org/resource/Leonardo_da_Vinci> ] .</pre></div>
+
+<p>Square brackets represent here a blank node. Predicate-object pairs within
+the square brackets are interpreted as triples with the blank node as
+subject. Lines starting with '#' represent
+comments. </p>
+
+<p>For more details about the syntax of Turtle please consult the Turtle specification [<cite><a href="#bib-TURTLE" class="bibref">TURTLE</a></cite>].</p>
+
+</section>
+
+<section rel="bibo:Chapter" resource="#section-trig" typeof="bibo:Chapter" id="section-trig">
+
+<h4 id="h4_section-trig" role="heading" aria-level="3"><span class="secno">5.1.3 </span>TriG</h4>
+
+<p>The syntax of Turtle supports only the specification of single
+graphs without a means for "naming" them. TriG [<cite><a href="#bib-TRIG" class="bibref">TRIG</a></cite>] is an
+<strong>extension of Turtle</strong> enabling the specification of
+multiple graphs in the form of an RDF dataset.</p>
+
+<div class="note"><div id="h_note_5" role="heading" aria-level="4" class="note-title"><span>Note</span></div><p class="">In RDF 1.1 any legal Turtle document is a legal TriG
+document. One could view it as one language. The names Turtle and TriG
+still exist for historical reasons.</p></div>
+
+<p>The <a href="#section-multiple-graphs">multiple-graphs version of our example</a>
+can be specified in TriG as follows:</p>
+
+<div class="example"><div class="example-title"><span>Example 10</span>: TriG</div><pre class="example" id="trig-example"><span class="linenum">01</span> BASE <http://example.org/>
+<span class="linenum">02</span> PREFIX foaf: <http://xmlns.com/foaf/0.1/>
+<span class="linenum">03</span> PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
+<span class="linenum">04</span> PREFIX schema: <http://schema.org/>
+<span class="linenum">05</span> PREFIX dcterms: <http://purl.org/dc/terms/>
+<span class="linenum">06</span> PREFIX wd: <http://www.wikidata.org/entity/>
+<span class="linenum">07</span>
+<span class="linenum">08</span> GRAPH <http://example.org/bob>
+<span class="linenum">09</span> {
+<span class="linenum">10</span> <bob#me>
+<span class="linenum">11</span> a foaf:Person ;
+<span class="linenum">12</span> foaf:knows <alice#me> ;
+<span class="linenum">13</span> schema:birthDate "1990-07-04"^^xsd:date ;
+<span class="linenum">14</span> foaf:topic_interest wd:Q12418 .
+<span class="linenum">15</span> }
+<span class="linenum">16</span>
+<span class="linenum">17</span> GRAPH <https://www.wikidata.org/wiki/Special:EntityData/Q12418>
+<span class="linenum">18</span> {
+<span class="linenum">19</span> wd:Q12418
+<span class="linenum">20</span> dcterms:title "Mona Lisa" ;
+<span class="linenum">21</span> dcterms:creator <http://dbpedia.org/resource/Leonardo_da_Vinci> .
+<span class="linenum">22</span>
+<span class="linenum">23</span> <http://data.europeana.eu/item/04802/243FA8618938F4117025F17A8B813C5F9AA4D619>
+<span class="linenum">24</span> dcterms:subject wd:Q12418 .
+<span class="linenum">25</span> }
+<span class="linenum">26</span>
+<span class="linenum">27</span> <http://example.org/bob>
+<span class="linenum">28</span> dcterms:publisher <http://example.org> ;
+<span class="linenum">29</span> dcterms:rights <http://creativecommons.org/licenses/by/3.0/> .</pre></div>
+
+ <p>This RDF dataset contains two named graphs. Lines 8 and 17 list
+ the names of these two graphs. The triples in the named graph are
+ placed in between matching curly braces (lines 9 & 15, 18 &
+ 25). Optionally you can precede the graph name with the keyword
+ <code>GRAPH</code>. This may improve readability, but it is mainly
+ introduced for alignment with SPARQL Update [<cite><a href="#bib-SPARQL11-UPDATE" class="bibref">SPARQL11-UPDATE</a></cite>]. </p>
+
+ <p>The syntax of the triples and of the directives at the top conforms to
+ the Turtle syntax.</p>
+
+ <p>The two triples specified on lines 27-29 are not part of any
+ named graph. Together they form the unnamed ("default") graph of this RDF
+ dataset.</p>
+
+ <p>The figure below shows the triples resulting from this example.</p>
+
+ <figure id="fig5">
+ <img style="width: 75%" src="example-multiple-graphs-iris.jpg" alt="Triples resulting from the TriG example">
+ <figcaption>Fig. <span class="figno">5</span> <span class="fig-title">Triples resulting from the TriG example</span></figcaption>
+ </figure>
+</section>
+
+<section rel="bibo:Chapter" resource="#section-n-quads" typeof="bibo:Chapter" id="section-n-quads">
+
+<h4 id="h4_section-n-quads" role="heading" aria-level="3"><span class="secno">5.1.4 </span>N-Quads</h4>
+
+<p>N-Quads [<cite><a href="#bib-N-QUADS" class="bibref">N-QUADS</a></cite>] is a simple extension to N-Triples to enable the exchange of RDF
+datasets. N-Quads allows one to add a fourth element to a line, capturing
+the graph IRI of the triple described on that line. Here is the
+N-Quads version of the TriG example above:</p>
+
+<div class="example"><div class="example-title"><span>Example 11</span>: N-Quads</div><pre class="example" id="n-quads-example"><span class="linenum">01</span> <http://example.org/bob#me> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://xmlns.com/foaf/0.1/Person> <http://example.org/bob> .
+<span class="linenum">02</span> <http://example.org/bob#me> <http://xmlns.com/foaf/0.1/knows> <http://example.org/alice#me> <http://example.org/bob> .
+<span class="linenum">03</span> <http://example.org/bob#me> <http://schema.org/birthDate> "1990-07-04"^^<http://www.w3.org/2001/XMLSchema#date> <http://example.org/bob> .
+<span class="linenum">04</span> <http://example.org/bob#me> <http://xmlns.com/foaf/0.1/topic_interest> <http://www.wikidata.org/entity/Q12418> <http://example.org/bob> .
+<span class="linenum">05</span> <http://www.wikidata.org/entity/Q12418> <http://purl.org/dc/terms/title> "Mona Lisa" <https://www.wikidata.org/wiki/Special:EntityData/Q12418> .
+<span class="linenum">06</span> <http://www.wikidata.org/entity/Q12418> <http://purl.org/dc/terms/creator> <http://dbpedia.org/resource/Leonardo_da_Vinci> <https://www.wikidata.org/wiki/Special:EntityData/Q12418> .
+<span class="linenum">07</span> <http://data.europeana.eu/item/04802/243FA8618938F4117025F17A8B813C5F9AA4D619> <http://purl.org/dc/terms/subject> <http://www.wikidata.org/entity/Q12418> <https://www.wikidata.org/wiki/Special:EntityData/Q12418> .
+<span class="linenum">08</span> <http://example.org/bob> <http://purl.org/dc/terms/publisher> <http://example.org> .
+<span class="linenum">09</span> <http://example.org/bob> <http://purl.org/dc/terms/rights> <http://creativecommons.org/licenses/by/3.0/> .</pre></div>
+
+<p>The nine lines in the N-Quads example correspond to the nine
+arcs in <a class="fig-ref" href="#fig5">Fig. 5</a>. Lines 1-7 represent quads, where the first
+element constitutes the graph IRI. The part of the quad after the
+graph IRI specifies the
+subject, predicate and object of the statement, following the syntactic
+conventions of N-Triples. Lines 8 and 9 represent the statements in the unnamed (default)
+graph, which lack a fourth element and thus constitute regular triples. </p>
+
+<p></p><p>Like N-Triples, N-Quads is typically used for exchanging large RDF datasets and for
+processing RDF with line-oriented text processing tools. </p>
+
+</section>
+</section>
+
+<section rel="bibo:Chapter" resource="#section-json-ld" typeof="bibo:Chapter" id="section-json-ld">
+<h3 id="h3_section-json-ld" role="heading" aria-level="2"><span class="secno">5.2 </span>JSON-LD</h3>
+
+ <p>JSON-LD [<cite><a href="#bib-JSON-LD" class="bibref">JSON-LD</a></cite>]
+ provides a JSON syntax for RDF graphs and datasets.
+ JSON-LD can be used to transform JSON documents to RDF with
+ minimal changes. JSON-LD offers universal identifiers for
+ JSON objects, a mechanism in which a JSON document can refer to
+ an object described in another JSON document elsewhere on the
+ Web, as well as datatype and language handling. JSON-LD
+ also provides a way to serialize RDF datasets
+ through the use of the <code>@graph</code> keyword. </p>
+
+ <p>The following JSON-LD example encodes the graph of <a class="fig-ref" href="#fig4">Fig. 4</a>:</p>
+
+<p>
+
+ </p><div class="example"><div class="example-title"><span>Example 12</span>: JSON-LD</div><pre class="example"><span class="linenum">01</span> {
+<span class="linenum">02</span> "@context": "example-context.json",
+<span class="linenum">03</span> "@id": "http://example.org/bob#me",
+<span class="linenum">04</span> "@type": "Person",
+<span class="linenum">05</span> "birthdate": "1990-07-04",
+<span class="linenum">06</span> "knows": "http://example.org/alice#me",
+<span class="linenum">07</span> "interest": {
+<span class="linenum">08</span> "@id": "http://www.wikidata.org/entity/Q12418",
+<span class="linenum">09</span> "title": "Mona Lisa",
+<span class="linenum">10</span> "subject_of": "http://data.europeana.eu/item/04802/243FA8618938F4117025F17A8B813C5F9AA4D619",
+<span class="linenum">11</span> "creator": "http://dbpedia.org/resource/Leonardo_da_Vinci"
+<span class="linenum">12</span> }
+<span class="linenum">13</span> }</pre></div>
+
+ <p>The <code>@context</code> key on line 2
+ points to a JSON document
+ describing how the document can be mapped to an RDF graph (see below).
+ Each JSON object corresponds to an RDF resource. In this example
+ the main resource being described is
+ <code>http://example.org/bob#me</code>, as
+ specified on line 3, through the use of the <code>@id</code> keyword.
+ The <code>@id</code> keyword, when used as a key in a JSON-LD document, points
+ to an IRI identifying the resource corresponding to the current JSON object.
+ We describe the type of this resource on line 4, its birth date
+ on line 5 and one of its friends on line 6. From line 7 to 12 we describe
+ one of its interests, the Mona Lisa painting.</p>
+
+ <p>To describe this painting we create a
+ new JSON object on line 7 and associate it with the Mona Lisa IRI in Wikidata
+ on line 8. We then describe various properties of that painting
+ from line 9 to line 11. </p>
+
+ <p>The JSON-LD context used in this example is given below.</p>
+
+<div class="example"><div class="example-title"><span>Example 13</span>: JSON-LD context specification</div><pre class="example"><span class="linenum">01</span> {
+<span class="linenum">02</span> "@context": {
+<span class="linenum">03</span> "foaf": "http://xmlns.com/foaf/0.1/",
+<span class="linenum">04</span> "Person": "foaf:Person",
+<span class="linenum">05</span> "interest": "foaf:topic_interest",
+<span class="linenum">06</span> "knows": {
+<span class="linenum">07</span> "@id": "foaf:knows",
+<span class="linenum">08</span> "@type": "@id"
+<span class="linenum">09</span> },
+<span class="linenum">10</span> "birthdate": {
+<span class="linenum">11</span> "@id": "http://schema.org/birthDate",
+<span class="linenum">12</span> "@type": "http://www.w3.org/2001/XMLSchema#date"
+<span class="linenum">13</span> },
+<span class="linenum">14</span> "dcterms": "http://purl.org/dc/terms/",
+<span class="linenum">15</span> "title": "dcterms:title",
+<span class="linenum">16</span> "creator": {
+<span class="linenum">17</span> "@id": "dcterms:creator",
+<span class="linenum">18</span> "@type": "@id"
+<span class="linenum">19</span> },
+<span class="linenum">20</span> "subject_of": {
+<span class="linenum">21</span> "@reverse": "dcterms:subject",
+<span class="linenum">22</span> "@type": "@id"
+<span class="linenum">23</span> }
+<span class="linenum">24</span> }
+<span class="linenum">25</span> }</pre></div>
+
+ <p>This context describes how a JSON-LD document can be mapped
+ to an RDF graph. Lines 4 to 9 specify how to map
+ <code>Person</code>, <code>interest</code> and <code>knows</code>
+ to types and properties in the FOAF namespace defined
+ on line 3. We also specify on line 8 that the <code>knows</code>
+ key has a value that will be interpreted as an IRI, through
+ the use of the <code>@type</code> and <code>@id</code> keywords.</p>
+
+ <p>From line 10 to line 12 we map <code>birthdate</code> to
+ a schema.org property IRI and specify that its value can
+ be mapped to an <code>xsd:date</code> datatype. </p>
+
+ <p>From line 14 to line 23 we describe how to map
+ <code>title</code>, <code>creator</code> and <code>subject_of</code>
+ to Dublin Core property IRIs. The <code>@reverse</code>
+ keyword on line 21 is used to specify that, whenever we
+ encounter <code>"subject_of": "x"</code> in a JSON-LD document using this
+ context, we should map it to an RDF triple which subject is the <code>x</code>
+ IRI, which property is <code>dcterms:subject</code> and
+ which object is the resource corresponding to the parent JSON object.</p>
+
+</section>
+
+<section rel="bibo:Chapter" resource="#section-rdfa" typeof="bibo:Chapter" id="section-rdfa">
+<h3 id="h3_section-rdfa" role="heading" aria-level="2"><span class="secno">5.3 </span>RDFa</h3>
+
+<p>RDFa [<cite><a href="#bib-RDFA-PRIMER" class="bibref">RDFA-PRIMER</a></cite>] is an RDF syntax that can be used to embed RDF data within
+HTML and XML documents. This enables, for example, search engines to aggregate
+this data when crawling the Web and use it to enrich search
+results (see, e.g., <a href="http://schema.org">schema.org</a>
+and <a href="https://support.google.com/webmasters/answer/99170?hl=en">Rich
+Snippets</a>). </p>
+
+<p>The HTML example below encodes the
+RDF graph depicted in <a class="fig-ref" href="#fig4">Fig. 4</a>:</p>
+
+<div class="example"><div class="example-title"><span>Example 14</span>: RDFa</div><pre class="example" id="rdfa-example"><span class="linenum">01</span> <body prefix="foaf: http://xmlns.com/foaf/0.1/
+<span class="linenum">02</span> schema: http://schema.org/
+<span class="linenum">03</span> dcterms: http://purl.org/dc/terms/">
+<span class="linenum">04</span> <div resource="http://example.org/bob#me" typeof="foaf:Person">
+<span class="linenum">05</span> <p>
+<span class="linenum">06</span> Bob knows <a property="foaf:knows" href="http://example.org/alice#me">Alice</a>
+<span class="linenum">07</span> and was born on the <time property="schema:birthDate" datatype="xsd:date">1990-07-04</time>.
+<span class="linenum">08</span> </p>
+<span class="linenum">09</span> <p>
+<span class="linenum">10</span> Bob is interested in <span property="foaf:topic_interest"
+<span class="linenum">11</span> resource="http://www.wikidata.org/entity/Q12418">the Mona Lisa</span>.
+<span class="linenum">12</span> </p>
+<span class="linenum">13</span> </div>
+<span class="linenum">14</span> <div resource="http://www.wikidata.org/entity/Q12418">
+<span class="linenum">15</span> <p>
+<span class="linenum">16</span> The <span property="dcterms:title">Mona Lisa</span> was painted by
+<span class="linenum">17</span> <a property="dcterms:creator" href="http://dbpedia.org/resource/Leonardo_da_Vinci">Leonardo da Vinci</a>
+<span class="linenum">18</span> and is the subject of the video
+<span class="linenum">19</span> <a href="http://data.europeana.eu/item/04802/243FA8618938F4117025F17A8B813C5F9AA4D619">'La Joconde à Washington'</a>.
+<span class="linenum">20</span> </p>
+<span class="linenum">21</span> </div>
+<span class="linenum">22</span> <div resource="http://data.europeana.eu/item/04802/243FA8618938F4117025F17A8B813C5F9AA4D619">
+<span class="linenum">23</span> <link property="dcterms:subject" href="http://www.wikidata.org/entity/Q12418"/>
+<span class="linenum">24</span> </div>
+<span class="linenum">25</span> </body></pre></div>
+
+<p>The example above contains four special RDFa attributes to enable
+specification of RDF triples within HTML: <code>resource</code>,
+<code>property</code>, <code>typeof</code> and <code>prefix</code>.</p><p>
+
+</p><p>The <code>prefix</code> attribute in line 1 specifies IRI
+shorthands in a similar fashion as the Turtle prefixes. Strictly
+speaking, these particular prefixes could have been omitted, as RDFa has a
+list of <a href="http://www.w3.org/2011/rdfa-context/rdfa-1.1">predefined
+prefixes</a> which includes the ones used in this example.</p>
+
+<p>The <code>div</code> elements in lines 4 and 14 have a <code>resource</code>
+attribute specifying the IRI about which RDF statements can be
+made within this HTML element. The meaning of the <code>typeof</code>
+attribute in line 4 is similar to the <code>(is) a</code> shorthand in
+Turtle: the subject <code>http://example.org/bob#me</code> is an
+instance (<code>rdf:type</code>) of the class <code>foaf:Person</code>.</p><p>
+
+</p><p>In line 6 we see a <code>property</code> attribute; the value
+of this attribute (<code>foaf:knows</code>) is interpreted as an RDF
+property IRI; the value of the <code>href</code> attribute
+(<code>http://example.org/alice#me</code>) is
+interpreted here as the object of the triple. Thus, the RDF statement
+that results from line 6 is:</p><p>
+
+</p><pre><code><http://example.org/bob#me> <http://xmlns.com/foaf/0.1/knows> <http://example.org/alice#me> .</code>
+</pre>
+
+<p>In line 7 we see a triple with as object a literal value. The
+<code>property</code> attribute is specified here on the HTML
+<code>time</code> element. HTML requires that the content of the time
+element should be some valid <a href="http://www.w3.org/TR/html5/text-level-semantics.html#the-time-element">time
+value</a>. By using the built-in HTML semantics of the
+<code>time</code> element RDFa can interpret
+the value as an <code>xsd:date</code> without an explicit datatype declaration.</p><p>
+
+</p><p>In lines 10-11 we see the <code>resource</code> attribute also being used for
+specifying the object of a triple. This approach is used when the object is an
+IRI and the IRI itself is not part of the HTML content (such as an <code>href</code>
+attribute). Line 16 contains a second example of a literal ("Mona
+Lisa"), defined here as content of the <code>span</code> attribute. If
+RDFa cannot infer the datatype of the literal, it will assume the
+datatype to be <code>xsd:string</code>. </p>
+
+<p>It is not always possible to define RDF statements as part of the
+HTML content of the document. In that case it is possible to use HTML
+constructs that do not render content to specify a triple. An example
+can be found on lines 22-23. The HTML <code>link</code> element on
+line 23 is used here to specify what
+the subject of the Europeana video (line 22) is. </p>
+
+<p>The use of RDFa in this example is limited to RDFa Lite
+[<cite><a href="#bib-RDFA-LITE" class="bibref">RDFA-LITE</a></cite>]. For more information about RDFa please consult the RDFa
+Primer [<cite><a href="#bib-RDFA-PRIMER" class="bibref">RDFA-PRIMER</a></cite>].</p>
+
+</section>
+
+<section rel="bibo:Chapter" resource="#section-rdfxml" typeof="bibo:Chapter" id="section-rdfxml">
+
+<h3 id="h3_section-rdfxml" role="heading" aria-level="2"><span class="secno">5.4 </span>RDF/XML</h3>
+
+<p>RDF/XML [<cite><a href="#bib-RDF-SYNTAX-GRAMMAR" class="bibref">RDF-SYNTAX-GRAMMAR</a></cite>] provides an XML syntax for RDF
+graphs. When RDF was originally developed in the late 1990s, this was its
+only syntax, and some people still call this syntax "RDF". In 2001, a
+precursor to Turtle called "N3" was proposed, and gradually the other
+languages listed here have been adopted and standardized. </p>
+
+<p>The RDF/XML example below encodes the
+RDF graph depicted in <a class="fig-ref" href="#fig4">Fig. 4</a>:</p>
+
+<div class="example"><div class="example-title"><span>Example 15</span>: RDF/XML</div><pre class="example" id="rdf-xml-example"><span class="linenum">01</span> <?xml version="1.0" encoding="utf-8"?>
+<span class="linenum">02</span> <rdf:RDF
+<span class="linenum">03</span> xmlns:dcterms="http://purl.org/dc/terms/"
+<span class="linenum">04</span> xmlns:foaf="http://xmlns.com/foaf/0.1/"
+<span class="linenum">05</span> xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+<span class="linenum">06</span> xmlns:schema="http://schema.org/">
+<span class="linenum">07</span> <rdf:Description rdf:about="http://example.org/bob#me">
+<span class="linenum">08</span> <rdf:type rdf:resource="http://xmlns.com/foaf/0.1/Person"/>
+<span class="linenum">09</span> <schema:birthDate rdf:datatype="http://www.w3.org/2001/XMLSchema#date">1990-07-04</schema:birthDate>
+<span class="linenum">10</span> <foaf:knows rdf:resource="http://example.org/alice#me"/>
+<span class="linenum">11</span> <foaf:topic_interest rdf:resource="http://www.wikidata.org/entity/Q12418"/>
+<span class="linenum">12</span> </rdf:Description>
+<span class="linenum">13</span> <rdf:Description rdf:about="http://www.wikidata.org/entity/Q12418">
+<span class="linenum">14</span> <dcterms:title>Mona Lisa</dcterms:title>
+<span class="linenum">15</span> <dcterms:creator rdf:resource="http://dbpedia.org/resource/Leonardo_da_Vinci"/>
+<span class="linenum">16</span> </rdf:Description>
+<span class="linenum">17</span> <rdf:Description rdf:about="http://data.europeana.eu/item/04802/243FA8618938F4117025F17A8B813C5F9AA4D619">
+<span class="linenum">18</span> <dcterms:subject rdf:resource="http://www.wikidata.org/entity/Q12418"/>
+<span class="linenum">19</span> </rdf:Description>
+<span class="linenum">20</span> </rdf:RDF></pre></div>
+
+<p>In RDF/XML RDF triples are specified within an XML element
+<code>rdf:RDF</code> (lines 2 and 20). The attributes of the
+<code>rdf:RDF</code> start tag (lines 3-6) provide a shorthand for writing down
+names of XML elements and attributes. The XML element
+<code>rdf:Description</code> (short for
+<code>http://www.w3.org/1999/02/22-rdf-syntax-ns#Description</code>)
+is used to define sets of triples that have as subject the IRI
+specified by the <code>about</code> attribute. The first description
+block (line 7-12) has four sub-elements. The name of the subelement is
+an IRI representing an RDF property, e.g., <code>rdf:type</code> (line 8). Here, each
+subelement represents one triple.
+In cases where the object of the triple is also an IRI
+the property subelement has no content and the object IRI is specified
+using the <code>rdf:resource</code> attribute (lines 8, 10-11, 15 and
+18). For example, line 10 corresponds to the triple:</p>
+
+<pre><code><http://example.org/bob#me> <http://xmlns.com/foaf/0.1/knows> <http://example.org/alice#me> .</code>
+</pre>
+
+<p>When the object of the
+triple is a literal the literal value is entered as content of the
+property element (lines 9 and 14). The datatype is specified as
+attribute of the property element (line 9). If the datatype is
+omitted (line 14) and no language tag is present the literal is
+considered to have the datatype <code>xsd:string</code>.
+
+</p><p>The example shows the baseline syntax; please consult the RDF/XML
+document [<cite><a href="#bib-RDF11-XML" class="bibref">RDF11-XML</a></cite>] for a more in-depth treatment of the syntax. It
+might seem strange that the attribute values contain full IRIs,
+despite the fact that for some of these namespace prefixes were
+defined. This is because these prefixes can only be used for XML
+element and attribute names. </p>
+
+</section>
+</section>
+
+
+<section rel="bibo:Chapter" resource="#section-semantics" typeof="bibo:Chapter" id="section-semantics">
+
+ <!--OddPage--><h2 id="h2_section-semantics" role="heading" aria-level="1"><span class="secno">6. </span>Semantics of RDF Graphs</h2>
+
+ <p>An overarching goal in the use of RDF is to be able to
+ automatically merge useful information from multiple sources to
+ form a larger collection that is still coherent and useful. As a
+ starting point for this merging, all the information is conveyed
+ in the same simple style, subject-predicate-object triples, as
+ described above. To keep the information coherent, however, we
+ need more than just a standard syntax; we also need agreement
+ about the semantics of these triples. </p>
+
+ <p>By this point in the Primer, the reader is likely to have an
+ intuitive grasp of the semantics of RDF:</p>
+ <ol>
+ <li>The IRIs used to name the subject, predicate, and object are "global" in scope,
+ naming the same thing each time they are used.</li>
+ <li>Each triple is "true" exactly when the predicate relation actually exists between
+ the subject and the object.</li>
+ <li>An RDF graph is "true" exactly when all the triples in it are "true".</li>
+ </ol>
+ <p>These notions,
+ and others, are specified with mathematical precision in the RDF
+ Semantics document [<cite><a href="#bib-RDF11-MT" class="bibref">RDF11-MT</a></cite>].</p>
+
+ <p>One of the benefits of RDF having these declarative semantics
+ is that systems can make logical inferences. That is, given a
+ certain set of input triples which they accept as true, systems
+ can in some circumstances deduce that other triples must,
+ logically, also be true. We say the first set of triples "entails"
+ the additional triples. These systems, called "reasoners", can also
+ sometimes deduce that the given input triples contradict each
+ other. </p>
+
+ <p>Given the flexibility of RDF, where new vocabularies can be
+ created when people want to use new concepts, there are many
+ different kinds of reasoning one might want to do. When a
+ specific kind of reasoning seems to be useful in many different
+ applications, it can be documented as an <a href="http://www.w3.org/TR/rdf11-mt/#semantic-extensions-and-entailment-regimes">entailment regime</a>.
+ Several entailment regimes are specified in RDF Semantics. For
+ technical descriptions of some other entailment regimes and how to
+ use these with SPARQL, see [<cite><a href="#bib-SPARQL11-ENTAILMENT" class="bibref">SPARQL11-ENTAILMENT</a></cite>].
+ Note that some
+ entailment regimes are fairly easy to implement and reasoning can
+ be done quickly, while others require sophisticated
+ techniques to implement efficiently. </p>
+
+ <p>As a sample entailment, consider the following two statements:</p>
+ <pre> <code>ex:bob foaf:knows ex:alice .</code>
+ <code>foaf:knows rdfs:domain foaf:Person .</code>
+ </pre>
+ <p>The RDF Semantics document tell us that from this graph it is legal to
+ derive the following triple:</p>
+ <pre> <code>ex:bob rdf:type foaf:Person .</code>
+ </pre>
+
+ <p>The derivation above is an example of an RDF Schema entailment [<cite><a href="#bib-RDF11-MT" class="bibref">RDF11-MT</a></cite>]. </p>
+
+ <p>The semantics of RDF also tell us that the triple:</p>
+ <pre> <code>ex:bob ex:age "forty"^^xsd:integer . </code>
+ </pre>
+ <p>leads to a logical inconsistency, because the literal does not
+ abide by the constraints defined for the XML Schema datatype <a href="http://www.w3.org/TR/xmlschema11-2/#integer">integer</a>.</p>
+
+ <p>Note that RDF tools may not recognize all datatypes. As a
+ minimum, tools are required to support the datatypes for string literals
+ and language-tagged literals.</p>
+
+ <p>Unlike many other data
+ modeling languages, RDF Schema allows considerable modeling
+ freedom. For example, the same entity may be used
+ as both a class and a property. Also, there is no strict separation
+ between the world of "classes" and of "instances". Therefore, RDF
+ semantics views the following graph as valid:</p>
+
+ <pre> <code>ex:Jumbo rdf:type ex:Elephant .</code>
+ <code>ex:Elephant rdf:type ex:Species .</code>
+ </pre>
+ <p>So, an elephant can both be a class (with Jumbo as a sample
+ instance) and an instance (namely of the class of
+ animal species).</p>
+
+ <p>The examples in this section are just meant to give the reader
+some feeling about what the RDF Semantics brings you. Please consult
+[<cite><a href="#bib-RDF11-MT" class="bibref">RDF11-MT</a></cite>] for a complete description.</p>
+
+ </section>
+
+ <section rel="bibo:Chapter" resource="#section-data" typeof="bibo:Chapter" id="section-data">
+
+ <!--OddPage--><h2 id="h2_section-data" role="heading" aria-level="1"><span class="secno">7. </span>RDF Data</h2>
+
+ <p>RDF allows you to combine triples from any source into a graph
+ and process it as legal RDF. A large amount of RDF data is
+ available as Linked
+ Data [<cite><a href="#bib-LINKED-DATA" class="bibref">LINKED-DATA</a></cite>]. Datasets are being published and
+ interlinked on the Web using RDF, and many of them offer a
+ querying facility through SPARQL [<cite><a href="#bib-SPARQL11-OVERVIEW" class="bibref">SPARQL11-OVERVIEW</a></cite>]. Examples
+ of such datasets used in the examples above include:</p>
+
+ <ul>
+ <li><a href="http://www.wikidata.org/">Wikidata</a>, a free,
+ collaborative and multilingual database and ran by the
+ <a href="http://www.wikimedia.org/">Wikimedia Foundation</a>.</li>
+
+ <li><a href="http://dbpedia.org/">DBpedia</a>, publishing data extracted
+ from <a href="http://en.wikipedia.org/wiki/Help:Infobox">Wikipedia infoboxes</a>.</li>
+
+ <li><a href="http://www.w3.org/2006/03/wn/wn20/">WordNet</a>,
+ a lexical database of English terms, grouped in sets
+ of synonyms, with a range of semantic interrelations. Similar
+ databases exist for other languages.</li>
+
+ <li><a href="http://www.europeana.eu/">Europeana</a>, publishing
+ data about cultural objects from a large number of European
+ institutions.</li>
+
+ <li><a href="http://viaf.org/">VIAF</a>, publishing data about
+ people, works and geographic places from a number of national
+ libraries and other agencies.</li>
+ </ul>
+
+ <p>A list of datasets available as Linked Data is maintained at
+ <a href="http://datahub.io/dataset">datahub.io</a>.</p>
+
+ <p>A number of vocabulary terms have become popular for
+ recording links between RDF data sources. An example is the
+ <code>sameAs</code> property provided by the OWL vocabulary. This
+ property can be used to indicate that two IRIs point in fact
+ to the same resource. This is useful because different publishers
+ may use different identifiers to denote the same thing. For
+ example, VIAF (see above) also has an IRI denoting Leonardo da
+ Vinci. With the help of <code>owl:sameAs</code> we can record this
+ information:</p>
+
+ <div class="example"><div class="example-title"><span>Example 16</span>: Link between datasets</div><pre class="example"><http://dbpedia.org/resource/Leonardo_da_Vinci>
+ owl:sameAs <http://viaf.org/viaf/24604287/> .</pre></div>
+
+ <p>Such links can be deployed by RDF data-processing
+ software, for example by merging or comparing RDF data of
+ IRIs that point to the same resource. </p>
+
+ </section>
+
+ <section rel="bibo:Chapter" resource="#section-conclusion" typeof="bibo:Chapter" id="section-conclusion">
+ <!--OddPage--><h2 id="h2_section-conclusion" role="heading" aria-level="1"><span class="secno">8. </span>More Information</h2>
+
+ <p>This concludes our brief introduction into RDF. Please consult
+ the references to get more detailed information. You might also
+ want to take a look at the <a href="http://www.w3.org/standards/semanticweb/data"><abbr title="World Wide Web Consortium">W3C</abbr> Linked Data page</a>. </p>
+
+ </section>
+
+ <section rel="bibo:Chapter" resource="#section-Acknowledgments" typeof="bibo:Chapter" id="section-Acknowledgments" class="appendix">
+ <!--OddPage--><h2 id="h2_section-Acknowledgments" role="heading" aria-level="1"><span class="secno">A. </span>Acknowledgments</h2>
+
+ <p>Antoine Isaac provided many examples, including the
+ different syntactic forms. Pierre-Antoine Champin provided one of
+ the JSON-LD examples. Andrew Wood designed the
+ diagrams. Sandro Hawke wrote the first part of the section on RDF
+ semantics. </p><p>
+ </p><p>We are grateful for the comments provided by (in
+ alphabetical order) Gareth Adams, Thomas Baker, Dan Brickley, Pierre-Antoine
+ Champin, Bob DuCharme, Sandro Hawke, Patrick
+ Hayes, Ivan Herman, Kingsley Idehen, Antoine Isaac, Markus Lanthaler, and David Wood. </p>
+
+
+<p>The introduction of this document contains a number of sentences from the
+ 2004 Primer [<cite><a href="#bib-RDF-PRIMER" class="bibref">RDF-PRIMER</a></cite>]. For the rest the RDF 1.1 Primer is a completely
+ new document.</p>
+
+</section>
+
+<section rel="bibo:Chapter" resource="#section-Changes" typeof="bibo:Chapter" id="section-Changes" class="appendix">
+
+<!--OddPage--><h2 id="h2_section-Changes" role="heading" aria-level="1"><span class="secno">B. </span>Changes since the previous publication</h2>
+<ul>
+ <li>Small editorial issues fixed (including three listed
+ <a href="http://www.w3.org/2014/rdf1.1-errata">errata</a>).</li>
+ <li>Link to Japanese translation added.</li>
+</ul>
+</section>
+
+
+
+<section rel="bibo:Chapter" resource="#references" typeof="bibo:Chapter" id="references" class="appendix"><!--OddPage--><h2 id="h2_references" role="heading" aria-level="1"><span class="secno">C. </span>References</h2><section rel="bibo:Chapter" resource="#informative-references" typeof="bibo:Chapter" id="informative-references"><h3 id="h3_informative-references" role="heading" aria-level="2"><span class="secno">C.1 </span>Informative references</h3><dl about="" class="bibliography"><dt id="bib-JSON-LD">[JSON-LD]</dt><dd rel="dcterms:references">Manu Sporny, Gregg Kellogg, Markus Lanthaler, Editors. <cite><a href="http://www.w3.org/TR/json-ld/">JSON-LD 1.0</a></cite>. 16 January 2014. W3C Recommendation. URL: <a href="http://www.w3.org/TR/json-ld/">http://www.w3.org/TR/json-ld/</a>
+</dd><dt id="bib-LINKED-DATA">[LINKED-DATA]</dt><dd rel="dcterms:references">Tim Berners-Lee. <cite><a href="http://www.w3.org/DesignIssues/LinkedData.html">Linked Data</a></cite>. Personal View, imperfect but published. URL: <a href="http://www.w3.org/DesignIssues/LinkedData.html">http://www.w3.org/DesignIssues/LinkedData.html</a>
+</dd><dt id="bib-N-QUADS">[N-QUADS]</dt><dd rel="dcterms:references">Gavin Carothers. <cite><a href="http://www.w3.org/TR/2014/REC-n-quads-20140225/">RDF 1.1 N-Quads</a></cite>. W3C Recommendation, 25 February 2014. URL: <a href="http://www.w3.org/TR/2014/REC-n-quads-20140225/">http://www.w3.org/TR/2014/REC-n-quads-20140225/</a>. The latest edition is available at <a href="http://www.w3.org/TR/n-quads/">http://www.w3.org/TR/n-quads/</a>
+</dd><dt id="bib-N-TRIPLES">[N-TRIPLES]</dt><dd rel="dcterms:references">Gavin Carothers, Andy Seabourne. <cite><a href="http://www.w3.org/TR/2014/REC-n-triples-20140225/">RDF 1.1 N-Triples</a></cite>. W3C Recommendation, 25 February 2014. URL: <a href="http://www.w3.org/TR/2014/REC-n-triples-20140225/">http://www.w3.org/TR/2014/REC-n-triples-20140225/</a>. The latest edition is available at <a href="http://www.w3.org/TR/n-triples/">http://www.w3.org/TR/n-triples/</a>
+</dd><dt id="bib-OWL2-OVERVIEW">[OWL2-OVERVIEW]</dt><dd rel="dcterms:references">W3C OWL Working Group. <a href="http://www.w3.org/TR/owl2-overview/"><cite>OWL 2 Web Ontology Language Document Overview (Second Edition)</cite></a>. 11 December 2012. W3C Recommendation. URL: <a href="http://www.w3.org/TR/owl2-overview/">http://www.w3.org/TR/owl2-overview/</a>
+</dd><dt id="bib-RDF-PRIMER">[RDF-PRIMER]</dt><dd rel="dcterms:references">Frank Manola; Eric Miller. <a href="http://www.w3.org/TR/rdf-primer/"><cite>RDF Primer</cite></a>. 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/rdf-primer/">http://www.w3.org/TR/rdf-primer/</a>
+</dd><dt id="bib-RDF-SYNTAX-GRAMMAR">[RDF-SYNTAX-GRAMMAR]</dt><dd rel="dcterms:references">Fabien Gandon; Guus Schreiber. <a href="http://www.w3.org/TR/rdf-syntax-grammar/"><cite>RDF 1.1 XML Syntax</cite></a>. 25 February 2014. W3C Recommendation. URL: <a href="http://www.w3.org/TR/rdf-syntax-grammar/">http://www.w3.org/TR/rdf-syntax-grammar/</a>
+</dd><dt id="bib-RDF11-CONCEPTS">[RDF11-CONCEPTS]</dt><dd rel="dcterms:references">Richard Cyganiak, David Wood, Markus Lanthaler. <cite><a href="http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/">RDF 1.1 Concepts and Abstract Syntax.</a></cite> W3C Recommendation, 25 February 2014. URL: <a href="http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/">http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/</a>. The latest edition is available at <a href="http://www.w3.org/TR/rdf11-concepts/">http://www.w3.org/TR/rdf11-concepts/</a>
+</dd><dt id="bib-RDF11-DATASETS">[RDF11-DATASETS]</dt><dd rel="dcterms:references">Antoine Zimmermann. <cite><a href="http://www.w3.org/TR/2014/NOTE-rdf11-datasets-20140225/">RDF 1.1: On Semantics of RDF Datasets</a></cite>. W3C Working Group Note, 25 February 2014. The latest version is available at <a href="http://www.w3.org/TR/rdf11-datasets/">http://www.w3.org/TR/rdf11-datasets/</a>.
+</dd><dt id="bib-RDF11-MT">[RDF11-MT]</dt><dd rel="dcterms:references">Patrick J. Hayes, Peter F. Patel-Schneider. <cite><a href="http://www.w3.org/TR/2014/REC-rdf11-mt-20140225/">RDF 1.1 Semantics.</a></cite> W3C Recommendation, 25 February 2014. URL: <a href="http://www.w3.org/TR/2014/REC-rdf11-mt-20140225/">http://www.w3.org/TR/2014/REC-rdf11-mt-20140225/</a>. The latest edition is available at <a href="http://www.w3.org/TR/rdf11-mt/">http://www.w3.org/TR/rdf11-mt/</a>
+</dd><dt id="bib-RDF11-NEW">[RDF11-NEW]</dt><dd rel="dcterms:references">David Wood. <cite><a href="http://www.w3.org/TR/2014/NOTE-rdf11-new-20140225/">What’s New in RDF 1.1</a></cite>. W3C Working Group Note, 25 February 2014. The latest version is available at <a href="http://www.w3.org/TR/rdf11-new/">http://www.w3.org/TR/rdf11-new/</a>.
+</dd><dt id="bib-RDF11-SCHEMA">[RDF11-SCHEMA]</dt><dd rel="dcterms:references">Dan Brickley, R. V. Guha. <cite><a href="http://www.w3.org/TR/2014/REC-rdf-schema-20140225/">RDF Schema 1.1</a></cite>. W3C Recommendation, 25 February 2014. URL: <a href="http://www.w3.org/TR/2014/REC-rdf-schema-20140225/">http://www.w3.org/TR/2014/REC-rdf-schema-20140225/</a>. The latest published version is available at <a href="http://www.w3.org/TR/rdf-schema/">http://www.w3.org/TR/rdf-schema/</a>.
+</dd><dt id="bib-RDF11-XML">[RDF11-XML]</dt><dd rel="dcterms:references">Fabien Gandon, Guus Schreiber. <cite><a href="http://www.w3.org/TR/2014/REC-rdf-syntax-grammar-20140225/">RDF 1.1 XML Syntax</a></cite>. W3C Recommendation, 25 February 2014. URL: <a href="http://www.w3.org/TR/2014/REC-rdf-syntax-grammar-20140225/">http://www.w3.org/TR/2014/REC-rdf-syntax-grammar-20140225/</a>. The latest published version is available at <a href="http://www.w3.org/TR/rdf-syntax-grammar/">http://www.w3.org/TR/rdf-syntax-grammar/</a>.
+</dd><dt id="bib-RDFA-LITE">[RDFA-LITE]</dt><dd rel="dcterms:references">Manu Sporny. <a href="http://www.w3.org/TR/rdfa-lite/"><cite>RDFa Lite 1.1</cite></a>. 7 June 2012. W3C Recommendation. URL: <a href="http://www.w3.org/TR/rdfa-lite/">http://www.w3.org/TR/rdfa-lite/</a>
+</dd><dt id="bib-RDFA-PRIMER">[RDFA-PRIMER]</dt><dd rel="dcterms:references">Ivan Herman; Ben Adida; Manu Sporny; Mark Birbeck. <a href="http://www.w3.org/TR/rdfa-primer/"><cite>RDFa 1.1 Primer - Second Edition</cite></a>. 22 August 2013. W3C Note. URL: <a href="http://www.w3.org/TR/rdfa-primer/">http://www.w3.org/TR/rdfa-primer/</a>
+</dd><dt id="bib-RFC3987">[RFC3987]</dt><dd rel="dcterms:references">M. Dürst; M. Suignard. <a href="http://www.ietf.org/rfc/rfc3987.txt"><cite>Internationalized Resource Identifiers (IRIs)</cite></a>. January 2005. RFC. URL: <a href="http://www.ietf.org/rfc/rfc3987.txt">http://www.ietf.org/rfc/rfc3987.txt</a>
+</dd><dt id="bib-SPARQL11-ENTAILMENT">[SPARQL11-ENTAILMENT]</dt><dd rel="dcterms:references">Birte Glimm; Chimezie Ogbuji. <a href="http://www.w3.org/TR/sparql11-entailment/"><cite>SPARQL 1.1 Entailment Regimes</cite></a>. 21 March 2013. W3C Recommendation. URL: <a href="http://www.w3.org/TR/sparql11-entailment/">http://www.w3.org/TR/sparql11-entailment/</a>
+</dd><dt id="bib-SPARQL11-OVERVIEW">[SPARQL11-OVERVIEW]</dt><dd rel="dcterms:references">The W3C SPARQL Working Group. <a href="http://www.w3.org/TR/sparql11-overview/"><cite>SPARQL 1.1 Overview</cite></a>. 21 March 2013. W3C Recommendation. URL: <a href="http://www.w3.org/TR/sparql11-overview/">http://www.w3.org/TR/sparql11-overview/</a>
+</dd><dt id="bib-SPARQL11-UPDATE">[SPARQL11-UPDATE]</dt><dd rel="dcterms:references">Paul Gearon; Alexandre Passant; Axel Polleres. <a href="http://www.w3.org/TR/sparql11-update/"><cite>SPARQL 1.1 Update</cite></a>. 21 March 2013. W3C Recommendation. URL: <a href="http://www.w3.org/TR/sparql11-update/">http://www.w3.org/TR/sparql11-update/</a>
+</dd><dt id="bib-TRIG">[TRIG]</dt><dd rel="dcterms:references">Gavin Carothers, Andy Seaborne. <cite><a href="http://www.w3.org/TR/2014/REC-trig-20140225/">TriG: RDF Dataset Language</a></cite>. W3C Recommendation, 25 February 2014. URL: <a href="http://www.w3.org/TR/2014/REC-trig-20140225/">http://www.w3.org/TR/2014/REC-trig-20140225/</a>. The latest edition is available at <a href="http://www.w3.org/TR/trig/">http://www.w3.org/TR/trig/</a>
+</dd><dt id="bib-TURTLE">[TURTLE]</dt><dd rel="dcterms:references">Eric Prud'hommeaux, Gavin Carothers. <cite><a href="http://www.w3.org/TR/2014/REC-turtle-20140225/">RDF 1.1 Turtle: Terse RDF Triple Language.</a></cite> W3C Recommendation, 25 February 2014. URL: <a href="http://www.w3.org/TR/2014/REC-turtle-20140225/">http://www.w3.org/TR/2014/REC-turtle-20140225/</a>. The latest edition is available at <a href="http://www.w3.org/TR/turtle/">http://www.w3.org/TR/turtle/</a>
+</dd></dl></section></section></body></html>
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