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| <h1 class="title">SPARQL Tutorial - Datasets</h1> |
| |
| |
| <main class="d-flex flex-xl-row flex-column"> |
| |
| <aside class="text-muted align-self-start mb-3 p-0 d-xl-none d-block"> |
| <h2 class="h6 sticky-top m-0 p-2 bg-body-tertiary">On this page</h2> |
| <nav id="TableOfContents"> |
| <ul> |
| <li><a href="#querying-datasets">Querying datasets</a> |
| <ul> |
| <li><a href="#example-data">Example Data</a></li> |
| <li><a href="#accessing-the-dataset">Accessing the Dataset</a></li> |
| <li><a href="#querying-a-specific-graph">Querying a specific graph</a></li> |
| <li><a href="#querying-to-find-data-from-graphs-that-match-a-pattern">Querying to find data from graphs that match a pattern</a></li> |
| </ul> |
| </li> |
| <li><a href="#describing-rdf-datasets---from-and-from-named">Describing RDF Datasets - <code>FROM</code> and <code>FROM NAMED</code></a></li> |
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| </aside> |
| <article class="flex-column me-lg-4"> |
| <p>This section covers RDF Datasets - an RDF Dataset is the unit that |
| is queried by a SPARQL query. It consists of a default graph, and a |
| number of named graphs.</p> |
| <h2 id="querying-datasets">Querying datasets</h2> |
| <p>The graph matching operation |
| (<a href="sparql_basic_patterns.html">basic patterns</a>, |
| <a href="sparql_optionals.html"><code>OPTIONAL</code>s</a>, and <a href="sparql_union.html"><code>UNION</code>s</a>) work on |
| one RDF graph. This starts out being the default graph of the |
| dataset but it can be changed by the <code>GRAPH</code> keyword.</p> |
| <pre><code>GRAPH uri { ... pattern ... } |
| |
| GRAPH var { ... pattern ... } |
| </code></pre> |
| <p>If a URI is given, the pattern will be matched against the graph in |
| the dataset with that name - if there isn’t one, the <code>GRAPH</code> clause |
| fails to match at all.</p> |
| <p>If a variable is given, all the named graphs (not the default |
| graph) are tried. The variable may be used elsewhere so that if, |
| during execution, its value is already known for a solution, only |
| the specific named graph is tried.</p> |
| <h3 id="example-data">Example Data</h3> |
| <p>An RDF dataset can take a variety of forms. Two common setups are |
| to have the default graph being the union (the RDF merge) of all |
| the named graphs or to have the default graph be an inventory of |
| the named graphs (where they came from, when they were read etc). |
| There are no limitations - one graph can be included twice under |
| different names, or some graphs may share triples with others.</p> |
| <p>In the examples below we will use the following dataset that might |
| occur for an RDF aggregator of book details:</p> |
| <p>Default graph (<a href="sparql_data/ds-dft.ttl">ds-dft.ttl</a>):</p> |
| <pre><code>@prefix dc: <http://purl.org/dc/elements/1.1/> . |
| @prefix xsd: <http://www.w3.org/2001/XMLSchema#> . |
| |
| <ds-ng-1.ttl> dc:date "2005-07-14T03:18:56+0100"^^xsd:dateTime . |
| <ds-ng-2.ttl> dc:date "2005-09-22T05:53:05+0100"^^xsd:dateTime . |
| </code></pre> |
| <p>Named graph (<a href="sparql_data/ds-ng-1.ttl">ds-ng-1.ttl</a>):</p> |
| <pre><code>@prefix dc: <http://purl.org/dc/elements/1.1/> . |
| |
| [] dc:title "Harry Potter and the Philospher's Stone" . |
| [] dc:title "Harry Potter and the Chamber of Secrets" . |
| </code></pre> |
| <p>Named graph (<a href="sparql_data/ds-ng-2.ttl">ds-ng-2.ttl</a>):</p> |
| <pre><code>@prefix dc: <http://purl.org/dc/elements/1.1/> . |
| |
| [] dc:title "Harry Potter and the Sorcerer's Stone" . |
| [] dc:title "Harry Potter and the Chamber of Secrets" . |
| </code></pre> |
| <p>That is, we have two small graphs describing some books, and we |
| have a default graph which records when these graphs were last |
| read.</p> |
| <p>Queries can be run with the command line application (this would be |
| all one line):</p> |
| <pre><code>java -cp ... arq.sparql |
| --graph ds-dft.ttl --namedgraph ds-ng-1.ttl --namedgraph ds-ng-2.ttl |
| --query query file |
| </code></pre> |
| <p>Datasets don’t have to be created just for the lifetime of the query. |
| They can be created and stored in a database, as would be more |
| usual for an aggregator application.</p> |
| <h3 id="accessing-the-dataset">Accessing the Dataset</h3> |
| <p>The first example just accesses the default graph |
| (<a href="sparql_data/q-ds-1.rq">q-ds-1.rq</a>):</p> |
| <pre><code>PREFIX xsd: <http://www.w3.org/2001/XMLSchema#> |
| PREFIX dc: <http://purl.org/dc/elements/1.1/> |
| PREFIX : <.> |
| |
| SELECT * |
| { ?s ?p ?o } |
| </code></pre> |
| <p>(The “<code>PREFIX : <.></code>” just helps format the output)</p> |
| <pre><code>---------------------------------------------------------------------- |
| | s | p | o | |
| ====================================================================== |
| | :ds-ng-2.ttl | dc:date | "2005-09-22T05:53:05+01:00"^^xsd:dateTime | |
| | :ds-ng-1.ttl | dc:date | "2005-07-14T03:18:56+01:00"^^xsd:dateTime | |
| ---------------------------------------------------------------------- |
| </code></pre> |
| <p>This is the default graph only - nothing from the named graphs |
| because they aren’t queried unless explicitly indicated via |
| <code>GRAPH</code>.</p> |
| <p>We can query for all triples by querying the default graph and the |
| named graphs (<a href="sparql_data/q-ds-2.rq">q-ds-2.rq</a>):</p> |
| <pre><code>PREFIX xsd: <http://www.w3.org/2001/XMLSchema#> |
| PREFIX dc: <http://purl.org/dc/elements/1.1/> |
| PREFIX : <.> |
| |
| SELECT * |
| { |
| { ?s ?p ?o } UNION { GRAPH ?g { ?s ?p ?o } } |
| } |
| </code></pre> |
| <p>giving:</p> |
| <pre><code>--------------------------------------------------------------------------------------- |
| | s | p | o | g | |
| ======================================================================================= |
| | :ds-ng-2.ttl | dc:date | "2005-09-22T05:53:05+01:00"^^xsd:dateTime | | |
| | :ds-ng-1.ttl | dc:date | "2005-07-14T03:18:56+01:00"^^xsd:dateTime | | |
| | _:b0 | dc:title | "Harry Potter and the Sorcerer's Stone" | :ds-ng-2.ttl | |
| | _:b1 | dc:title | "Harry Potter and the Chamber of Secrets" | :ds-ng-2.ttl | |
| | _:b2 | dc:title | "Harry Potter and the Chamber of Secrets" | :ds-ng-1.ttl | |
| | _:b3 | dc:title | "Harry Potter and the Philospher's Stone" | :ds-ng-1.ttl | |
| --------------------------------------------------------------------------------------- |
| </code></pre> |
| <h3 id="querying-a-specific-graph">Querying a specific graph</h3> |
| <p>If the application knows the name graph, it can directly ask a |
| query such as finding all the titles in a given graph |
| (<a href="sparql_data/q-ds-3.rq">q-ds-3.rq</a>):</p> |
| <pre><code>PREFIX dc: <http://purl.org/dc/elements/1.1/> |
| PREFIX : <.> |
| |
| SELECT ?title |
| { |
| GRAPH :ds-ng-2.ttl |
| { ?b dc:title ?title } |
| } |
| </code></pre> |
| <p>Results:</p> |
| <pre><code>--------------------------------------------- |
| | title | |
| ============================================= |
| | "Harry Potter and the Sorcerer's Stone" | |
| | "Harry Potter and the Chamber of Secrets" | |
| --------------------------------------------- |
| </code></pre> |
| <h3 id="querying-to-find-data-from-graphs-that-match-a-pattern">Querying to find data from graphs that match a pattern</h3> |
| <p>The name of the graphs to be queried can be determined with the |
| query itself. The same process for variables applies whether they |
| are part of a graph pattern or the <code>GRAPH</code> form. The query below |
| (<a href="sparql_data/q-ds-4.rq">q-ds-4.rq</a>) sets a condition on the variable used to |
| select named graphs, based on information in the default graph.</p> |
| <pre><code>PREFIX xsd: <http://www.w3.org/2001/XMLSchema#> |
| PREFIX dc: <http://purl.org/dc/elements/1.1/> |
| PREFIX : <.> |
| |
| SELECT ?date ?title |
| { |
| ?g dc:date ?date . FILTER (?date > "2005-08-01T00:00:00Z"^^xsd:dateTime ) |
| GRAPH ?g |
| { ?b dc:title ?title } |
| } |
| </code></pre> |
| <p>The results of executing this query on the example dataset are the |
| titles in one of the graphs, the one with the date later than 1 |
| August 2005.</p> |
| <pre><code>----------------------------------------------------------------------------------------- |
| | date | title | |
| ========================================================================================= |
| | "2005-09-22T05:53:05+01:00"^^xsd:dateTime | "Harry Potter and the Sorcerer's Stone" | |
| | "2005-09-22T05:53:05+01:00"^^xsd:dateTime | "Harry Potter and the Chamber of Secrets" | |
| ----------------------------------------------------------------------------------------- |
| </code></pre> |
| <h2 id="describing-rdf-datasets---from-and-from-named">Describing RDF Datasets - <code>FROM</code> and <code>FROM NAMED</code></h2> |
| <p>A query execution can be given the dataset when the execution |
| object is built or it can be described in the query itself. When |
| the details are on the command line, a temporary dataset is created |
| but an application can create datasets and then use them in many |
| queries.</p> |
| <p>When described in the query, <code>FROM <</code><em><code>url</code></em><code>></code> is used to identify |
| the contents to be in the default graph. There can be more than one |
| <code>FROM</code> clause and the default graph is result of reading each file |
| into the default graph. It is the RDF merge of the individual |
| graphs.</p> |
| <p>Don’t be confused by the fact the default graph is described by one |
| or more URLs in <code>FROM</code> clauses. This is where the data is read |
| from, not the name of the graph. As several FROM clauses can be |
| given, the data can be read in from several places but none of them |
| become the graph name.</p> |
| <p><code>FROM NAMED <</code><em><code>url</code></em><code>></code> is used to identify a named graph. The |
| graph is given the name <em>url</em> and the data is read from that |
| location. Multiple <code>FROM NAMED</code> clauses cause multiple graphs to be |
| added to the dataset.</p> |
| <p>For example, the query to find all the triples in both default |
| graph and named graphs could be written as |
| (<a href="sparql_data/q-ds-5.rq">q-ds-5.rq</a>):</p> |
| <pre><code>PREFIX xsd: <http://www.w3.org/2001/XMLSchema#> |
| PREFIX dc: <http://purl.org/dc/elements/1.1/> |
| PREFIX : <.> |
| |
| SELECT * |
| FROM <ds-dft.ttl> |
| FROM NAMED <ds-ng-1.ttl> |
| FROM NAMED <ds-ng-2.ttl> |
| { |
| { ?s ?p ?o } UNION { GRAPH ?g { ?s ?p ?o } } |
| } |
| </code></pre> |
| <p><a href="sparql_results.html">Next: results</a></p> |
| |
| </article> |
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| <li><a href="#querying-datasets">Querying datasets</a> |
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| <li><a href="#example-data">Example Data</a></li> |
| <li><a href="#accessing-the-dataset">Accessing the Dataset</a></li> |
| <li><a href="#querying-a-specific-graph">Querying a specific graph</a></li> |
| <li><a href="#querying-to-find-data-from-graphs-that-match-a-pattern">Querying to find data from graphs that match a pattern</a></li> |
| </ul> |
| </li> |
| <li><a href="#describing-rdf-datasets---from-and-from-named">Describing RDF Datasets - <code>FROM</code> and <code>FROM NAMED</code></a></li> |
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| |
| <script src="/js/popper.min.js.js" type="text/javascript"></script> |
| <script src="/js/bootstrap.min.js" type="text/javascript"></script> |
| <script src="/js/improve.js" type="text/javascript"></script> |
| |
| <script type="text/javascript"> |
| (function() { |
| 'use strict' |
| |
| |
| |
| const links = document.querySelectorAll(`a[href="${window.location.pathname}"]`) |
| if (links !== undefined && links !== null) { |
| for (const link of links) { |
| |
| link.classList.add('active') |
| let parentElement = link.parentElement |
| let count = 0 |
| const levelsLimit = 4 |
| |
| |
| |
| |
| |
| while (['UL', 'LI'].includes(parentElement.tagName) && count <= levelsLimit) { |
| if (parentElement.tagName === 'LI') { |
| |
| |
| |
| parentElement.querySelector('a:first-child').classList.add('active') |
| } |
| parentElement = parentElement.parentElement |
| count++ |
| } |
| } |
| } |
| })() |
| </script> |
| |
| </body> |
| </html> |
