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border-left-style: solid; } div.issue, div.note { padding: 1em 1.2em 0.5em; margin: 1em 0; position: relative; clear: both; } span.note, span.issue { padding: .1em .5em .15em; } .issue { border-color: #e05252; background: #fbe9e9; } .note { border-color: #52e052; background: #e9fbe9; } </style><link href="https://www.w3.org/StyleSheets/TR/W3C-WG-NOTE" rel="stylesheet"></head> <body id="respecDocument" role="document" class="h-entry"><div id="respecHeader" role="contentinfo" class="head"> <p> <a href="https://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="https://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="https://www.w3.org/TR/rdf11-primer/">http://www.w3.org/TR/rdf11-primer/</a></dd> <dt>Previous version:</dt> <dd><a href="https://www.w3.org/TR/2014/NOTE-rdf11-primer-20140225/" rel="dcterms:replaces">http://www.w3.org/TR/2014/NOTE-rdf11-primer-20140225/</a></dd> <dt>Latest Recommendation:</dt> <dd><a href="https://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="https://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="https://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2003-2014 <a href="https://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="https://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>, <a href="https://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and <a href="https://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="https://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>]. This document contains some minor editorial <a href="#section-Changes">fixes</a> of the Februay 2014 version.</p> <p> This document was published by the <a href="https://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="https://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="https://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="https://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential Claim(s)</a> must disclose the information in accordance with <a href="https://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"> <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="https://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"> <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="https://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"> <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>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="https://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="https://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="https://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="https://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>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="https://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="https://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="https://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="https://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="https://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"> <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="https://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="https://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="https://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="https://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="https://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="https://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="https://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="https://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"> <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="https://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 <a href="https://www.w3.org/TR/json-ld/#named-graphs">@graph</a> 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="https://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="https://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"> <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="https://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="https://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"> <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="https://www.wikidata.org/">Wikidata</a>, a free, collaborative and multilingual database and ran by the <a href="https://www.wikimedia.org/">Wikimedia Foundation</a>.</li> <li><a href="http://dbpedia.org/">DBpedia</a>, publishing data extracted from <a href="https://en.wikipedia.org/wiki/Help:Infobox">Wikipedia infoboxes</a>.</li> <li><a href="https://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"> <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="https://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"> <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"> <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="https://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"><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="https://www.w3.org/TR/json-ld/">JSON-LD 1.0</a></cite>. 16 January 2014. W3C Recommendation. URL: <a href="https://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="https://www.w3.org/DesignIssues/LinkedData.html">Linked Data</a></cite>. Personal View, imperfect but published. URL: <a href="https://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="https://www.w3.org/TR/2014/REC-n-quads-20140225/">RDF 1.1 N-Quads</a></cite>. W3C Recommendation, 25 February 2014. URL: <a href="https://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="https://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="https://www.w3.org/TR/2014/REC-n-triples-20140225/">RDF 1.1 N-Triples</a></cite>. W3C Recommendation, 25 February 2014. URL: <a href="https://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="https://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="https://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="https://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="https://www.w3.org/TR/rdf-primer/"><cite>RDF Primer</cite></a>. 10 February 2004. W3C Recommendation. URL: <a href="https://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="https://www.w3.org/TR/rdf-syntax-grammar/"><cite>RDF 1.1 XML Syntax</cite></a>. 25 February 2014. W3C Recommendation. URL: <a href="https://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="https://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="https://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="https://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="https://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="https://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="https://www.w3.org/TR/2014/REC-rdf11-mt-20140225/">RDF 1.1 Semantics.</a></cite> W3C Recommendation, 25 February 2014. URL: <a href="https://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="https://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="https://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="https://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="https://www.w3.org/TR/2014/REC-rdf-schema-20140225/">RDF Schema 1.1</a></cite>. W3C Recommendation, 25 February 2014. URL: <a href="https://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="https://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="https://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="https://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="https://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="https://www.w3.org/TR/rdfa-lite/"><cite>RDFa Lite 1.1</cite></a>. 7 June 2012. W3C Recommendation. URL: <a href="https://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="https://www.w3.org/TR/rdfa-primer/"><cite>RDFa 1.1 Primer - Second Edition</cite></a>. 22 August 2013. W3C Note. URL: <a href="https://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="https://www.w3.org/TR/sparql11-entailment/"><cite>SPARQL 1.1 Entailment Regimes</cite></a>. 21 March 2013. W3C Recommendation. URL: <a href="https://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="https://www.w3.org/TR/sparql11-overview/"><cite>SPARQL 1.1 Overview</cite></a>. 21 March 2013. W3C Recommendation. URL: <a href="https://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">Paula Gearon; Alexandre Passant; Axel Polleres. <a href="https://www.w3.org/TR/sparql11-update/"><cite>SPARQL 1.1 Update</cite></a>. 21 March 2013. W3C Recommendation. URL: <a href="https://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="https://www.w3.org/TR/2014/REC-trig-20140225/">TriG: RDF Dataset Language</a></cite>. W3C Recommendation, 25 February 2014. URL: <a href="https://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="https://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="https://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="https://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="https://www.w3.org/TR/turtle/">http://www.w3.org/TR/turtle/</a> </dd></dl></section></section><script src="https://www.w3.org/scripts/TR/fixup.js"></script></body></html>