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| <h1 class="title">Support of RDF-star</h1> |
| |
| <p><a href="https://w3c.github.io/rdf-star/">RDF-star</a> is an extension to RDF that provides |
| a way for one triple to refer to another triple. RDF* is the name of the |
| original work which is described in |
| <a href="https://blog.liu.se/olafhartig/2019/01/10/position-statement-rdf-star-and-sparql-star/">Olaf Hartig’s blog entry</a>.</p> |
| <p>Example:</p> |
| <div class="highlight"><pre style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-turtle" data-lang="turtle"><span style=""><<</span><span style="color:#bbb"> </span><span style="color:#00f;font-weight:bold">:</span><span style="color:#008000;font-weight:bold">john</span><span style="color:#bbb"> </span><span style="color:#00f;font-weight:bold">foaf:</span><span style="color:#008000;font-weight:bold">name</span><span style="color:#bbb"> </span><span style="color:#b44">"John Smith"</span><span style="color:#bbb"> </span><span style="">>></span><span style="color:#bbb"> </span><span style="color:#00f;font-weight:bold">dct:</span><span style="color:#008000;font-weight:bold">source</span><span style="color:#bbb"> </span><span style="color:#b8860b"><http://example/directory></span><span style="color:#bbb"> </span>.<span style="color:#bbb"> |
| </span></code></pre></div><p>The part <code><< :john foaf:name "John Smith" >></code> is a quoted triple and refers to the triple with subject <code>:john</code>, property <code>foaf:name</code> and object <code>"John Smith"</code>.</p> |
| <p>Triple terms can be in the subject or object position.</p> |
| <p>Jena provides support for RDF-star and the related SPARQL-star.</p> |
| <ul> |
| <li>Turtle, N-Triples, TriG and N-Quads extended for Triple Terms syntax, |
| input and output. There is no output in RDF/XML.</li> |
| <li>SPARQL extended with Triple Term syntax for graph matching.</li> |
| <li>SPARQL Result formats for JSON and XML extended to support quoted triples in results.</li> |
| <li>Support in the Model API.</li> |
| <li>Translation to and from RDF reification.</li> |
| </ul> |
| <p>All this is active by default in Fuseki.</p> |
| <p>The aim is to follow the definition of the <a href="https://w3c.github.io/rdf-star/">RDF-star community</a>.</p> |
| <p>Storage in databases <a href="/documentation/tdb">TDB1</a> and <a href="/documentation/tdb2/">TDB2</a> |
| as well as in-memory databases is supported.</p> |
| <h2 id="rdf-star">RDF-star</h2> |
| <p>RDF-star syntax for quoted triples is added to the parsers for Turtle, N-Triples, TriG and N-Quads.</p> |
| <p>Datasets may have graphs that have quoted triples that refer to triples anywhere, not just in the same graph.</p> |
| <h2 id="sparql-star">SPARQL-star</h2> |
| <p>Matches for quoted triples:</p> |
| <div class="highlight"><pre style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-sparql" data-lang="sparql"><span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#b8860b">?name</span> { <span style="color:#666"><<</span>:<span style="color:#008000;font-weight:bold">john</span> <span style="color:#00f;font-weight:bold">foaf</span>:<span style="color:#008000;font-weight:bold">name</span> <span style="color:#b8860b">?name</span> <span style="color:#666">>></span> <span style="color:#00f;font-weight:bold">dct</span>:<span style="color:#008000;font-weight:bold">source</span> <span style="color:#a0a000"><http://example/directory></span> } |
| </code></pre></div><p>Insert triples terms into the default graph to record the graph source.</p> |
| <div class="highlight"><pre style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-sparql" data-lang="sparql"><span style="color:#a2f;font-weight:bold">INSERT</span> { <span style="color:#666"><<</span><span style="color:#b8860b">?s</span> <span style="color:#b8860b">?p</span> <span style="color:#b8860b">?o</span><span style="color:#666">>></span> <span style="color:#00f;font-weight:bold">dct</span>:<span style="color:#008000;font-weight:bold">source</span> <span style="color:#a0a000"><http://example/directory></span> } |
| <span style="color:#a2f;font-weight:bold">WHERE</span> { |
| <span style="color:#a2f;font-weight:bold">GRAPH</span> <span style="color:#a0a000"><http://example/directory></span> { |
| <span style="color:#b8860b">?s</span> <span style="color:#b8860b">?p</span> <span style="color:#b8860b">?o</span> |
| } |
| } |
| </code></pre></div><p>Use in expressions:</p> |
| <div class="highlight"><pre style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-sparql" data-lang="sparql"><span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#b8860b">?t</span> { |
| <span style="color:#b8860b">?s</span> <span style="color:#b8860b">?p</span> <span style="color:#b8860b">?o</span> |
| <span style="color:#a2f;font-weight:bold">BIND</span>(<span style="color:#666"><<</span> <span style="color:#b8860b">?s</span> <span style="color:#b8860b">?p</span> <span style="color:#b8860b">?o</span><span style="color:#666">>></span> <span style="color:#a2f;font-weight:bold">AS</span> <span style="color:#b8860b">?t</span>) |
| } |
| </code></pre></div><div class="highlight"><pre style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-sparql" data-lang="sparql"><span style="color:#a2f;font-weight:bold">SELECT</span> (<span style="color:#666"><<</span> <span style="color:#b8860b">?s</span> <span style="color:#b8860b">?p</span> <span style="color:#b8860b">?o</span><span style="color:#666">>></span> <span style="color:#a2f;font-weight:bold">AS</span> <span style="color:#b8860b">?t</span>) { |
| <span style="color:#b8860b">?s</span> <span style="color:#b8860b">?p</span> <span style="color:#b8860b">?o</span> |
| } |
| </code></pre></div><h3 id="sparql-functions-related-to-quoted-triples">SPARQL Functions related to quoted triples</h3> |
| <p>These functions cause an expression error if passed the wrong type of arguments.</p> |
| <table> |
| <thead> |
| <tr> |
| <th>Function</th> |
| <th>Description</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td><code>TRIPLE(?s, ?p, ?o)</code></td> |
| <td>Create a quoted triple from s/p/o</td> |
| </tr> |
| <tr> |
| <td><code>isTRIPLE(?t)</code></td> |
| <td>Return true if the argument value is a quoted triple</td> |
| </tr> |
| <tr> |
| <td><code>SUBJECT(?t)</code></td> |
| <td>Return the subject of the quoted triple</td> |
| </tr> |
| <tr> |
| <td><code>PREDICATE(?t)</code></td> |
| <td>Return the predicate (property) of the quoted triple</td> |
| </tr> |
| <tr> |
| <td><code>OBJECT(?t)</code></td> |
| <td>Return the object of the quoted triple</td> |
| </tr> |
| </tbody> |
| </table> |
| <h3 id="sparql-results">SPARQL results</h3> |
| <p>The syntaxes for SPARQL results from a SELECT query, <code>application/sparql-results+json</code>, |
| <code>application/sparql-results+xml</code> are extended to include quoted triples:</p> |
| <p>The quoted triple <code><< _:b0 <http://example/p> 123 >></code> is encoded, in |
| <code>application/sparql-results+json</code> as:</p> |
| <div class="highlight"><pre style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-json" data-lang="json"> { |
| <span style="color:#008000;font-weight:bold">"type"</span>: <span style="color:#b44">"triple"</span> , |
| <span style="color:#008000;font-weight:bold">"value"</span>: { |
| <span style="color:#008000;font-weight:bold">"subject"</span>: { <span style="color:#008000;font-weight:bold">"type"</span>: <span style="color:#b44">"bnode"</span> , <span style="color:#008000;font-weight:bold">"value"</span>: <span style="color:#b44">"b0"</span> } , |
| <span style="color:#008000;font-weight:bold">"predicate"</span>: { <span style="color:#008000;font-weight:bold">"type"</span>: <span style="color:#b44">"uri"</span> , <span style="color:#008000;font-weight:bold">"value"</span>: <span style="color:#b44">"http://example/p"</span> } , |
| <span style="color:#008000;font-weight:bold">"object"</span>: { <span style="color:#008000;font-weight:bold">"type"</span>: <span style="color:#b44">"literal"</span> , <span style="color:#008000;font-weight:bold">"datatype"</span>: <span style="color:#b44">"http://www.w3.org/2001/XMLSchema#integer"</span> , <span style="color:#008000;font-weight:bold">"value"</span>: <span style="color:#b44">"123"</span> } |
| } |
| </code></pre></div><p>and similarly in <code>application/sparql-results+xml</code>:</p> |
| <div class="highlight"><pre style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4"><code class="language-xml" data-lang="xml"> <span style="color:#008000;font-weight:bold"><triple></span> |
| <span style="color:#008000;font-weight:bold"><subject></span> |
| <span style="color:#008000;font-weight:bold"><bnode></span>b0<span style="color:#008000;font-weight:bold"></bnode></span> |
| <span style="color:#008000;font-weight:bold"></subject></span> |
| <span style="color:#008000;font-weight:bold"><predicate></span> |
| <span style="color:#008000;font-weight:bold"><uri></span>http://example/p<span style="color:#008000;font-weight:bold"></uri></span> |
| <span style="color:#008000;font-weight:bold"></predicate></span> |
| <span style="color:#008000;font-weight:bold"><object></span> |
| <span style="color:#008000;font-weight:bold"><literal</span> <span style="color:#b44">datatype=</span><span style="color:#b44">"http://www.w3.org/2001/XMLSchema#integer"</span><span style="color:#008000;font-weight:bold">></span>123<span style="color:#008000;font-weight:bold"></literal></span> |
| <span style="color:#008000;font-weight:bold"></object></span> |
| <span style="color:#008000;font-weight:bold"></triple></span> |
| </code></pre></div><h2 id="model-api">Model API</h2> |
| <p>RDF-star quoted triples are treated as <code>Resource</code> to preserve the typed Model API. |
| They occur in the subject and object positions.</p> |
| <p>A <code>Resource</code> contains a <code>Statement</code> object if the underlying RDF term is an RDF-star quoted triple.</p> |
| <p>New methods include:</p> |
| <ul> |
| <li><code>Statement Resource.getStatement()</code></li> |
| <li><code>Resource Model.createResource(Statement)</code></li> |
| <li><code>Resource ResourceFactory.createStatement</code></li> |
| </ul> |
| <h2 id="reification">Reification</h2> |
| <p><code>org.apache.jena.system.RDFStar</code> provides functions to translate RDF-star into |
| RDF reification, and translate it back again to RDF-star.</p> |
| <p>Translating back to RDF-star relies on the consistency constraint that there is |
| only one reification for each unique quoted triple term.</p> |
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