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| <h1 class="title">SPARQL Tutorial - Alternatives in a Pattern</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="#union---two-ways-to-the-same-data">UNION - two ways to the same data</a></li> |
| <li><a href="#union---remembering-where-the-data-was-found">UNION - remembering where the data was found.</a></li> |
| <li><a href="#optional-and-union">OPTIONAL and UNION</a></li> |
| </ul> |
| </nav> |
| </aside> |
| <article class="flex-column me-lg-4"> |
| <p>Another way of dealing with the semi-structured data is to query |
| for one of a number of possibilities. This section covers <code>UNION</code> |
| patterns, where one of a number of possibilities is tried.</p> |
| <h2 id="union---two-ways-to-the-same-data">UNION - two ways to the same data</h2> |
| <p>Both the vCard vocabulary and the FOAF vocabulary have properties |
| for people’s names. In vCard, it is vCard:FN, the “formatted |
| name”, and in FOAF, it is foaf:name. In this section, we will look |
| at a small set of data where the names of people can be given by |
| either the FOAF or the vCard vocabulary.</p> |
| <p>Suppose we have <a href="sparql_data/vc-db-3.ttl">an RDF graph</a> that contains name |
| information using both the vCard and FOAF vocabularies.</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-turtle" data-lang="turtle"><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">@prefix</span><span style="color:#bbb"> </span><span style="color:#00f;font-weight:bold">foaf:</span><span style="color:#bbb"> </span><span style="color:#b8860b"><http://xmlns.com/foaf/0.1/></span><span style="color:#bbb"> </span>.<span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="color:#a2f;font-weight:bold">@prefix</span><span style="color:#bbb"> </span><span style="color:#00f;font-weight:bold">vcard:</span><span style="color:#bbb"> </span><span style="color:#b8860b"><http://www.w3.org/2001/vcard-rdf/3.0#></span><span style="color:#bbb"> </span>.<span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">_</span><span style="color:#00f;font-weight:bold">:</span><span style="color:#008000;font-weight:bold">a</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">"Matt Jones"</span><span style="color:#bbb"> </span>.<span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">_</span><span style="color:#00f;font-weight:bold">:</span><span style="color:#008000;font-weight:bold">b</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">"Sarah Jones"</span><span style="color:#bbb"> </span>.<span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">_</span><span style="color:#00f;font-weight:bold">:</span><span style="color:#008000;font-weight:bold">c</span><span style="color:#bbb"> </span><span style="color:#00f;font-weight:bold">vcard:</span><span style="color:#008000;font-weight:bold">FN</span><span style="color:#bbb"> </span><span style="color:#b44">"Becky Smith"</span><span style="color:#bbb"> </span>.<span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">_</span><span style="color:#00f;font-weight:bold">:</span><span style="color:#008000;font-weight:bold">d</span><span style="color:#bbb"> </span><span style="color:#00f;font-weight:bold">vcard:</span><span style="color:#008000;font-weight:bold">FN</span><span style="color:#bbb"> </span><span style="color:#b44">"John Smith"</span><span style="color:#bbb"> </span>.<span style="color:#bbb"> |
| </span></span></span></code></pre></div><p>A query to access the name information, when it can be in either |
| form, could be (<a href="sparql_data/q-union1.rq">q-union1.rq</a>):</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-sparql" data-lang="sparql"><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">PREFIX</span> <span style="color:#00f;font-weight:bold">foaf</span>: <span style="color:#a0a000"><http://xmlns.com/foaf/0.1/></span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">PREFIX</span> <span style="color:#00f;font-weight:bold">vCard</span>: <span style="color:#a0a000"><http://www.w3.org/2001/vcard-rdf/3.0#></span> |
| </span></span><span style="display:flex;"><span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#b8860b">?name</span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">WHERE</span> |
| </span></span><span style="display:flex;"><span>{ |
| </span></span><span style="display:flex;"><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:#a2f;font-weight:bold">UNION</span> { [] <span style="color:#00f;font-weight:bold">vCard</span>:<span style="color:#008000;font-weight:bold">FN</span> <span style="color:#b8860b">?name</span> } |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><p>This returns the results:</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-turtle" data-lang="turtle"><span style="display:flex;"><span><span style="">-----------------</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</span><span style="color:#bbb"> </span><span style="">name</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">=================</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</span><span style="color:#bbb"> </span><span style="color:#b44">"Matt Jones"</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</span><span style="color:#bbb"> </span><span style="color:#b44">"Sarah Jones"</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</span><span style="color:#bbb"> </span><span style="color:#b44">"Becky Smith"</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</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></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">-----------------</span><span style="color:#bbb"> |
| </span></span></span></code></pre></div><p>It didn’t matter which form of expression was used for the name, |
| the ?name variable is set. This can be achieved using a <code>FILTER</code> as |
| this query (<a href="sparql_data/q-union1alt.rq">q-union-1alt.rq</a>) shows:</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-sparql" data-lang="sparql"><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">PREFIX</span> <span style="color:#00f;font-weight:bold">foaf</span>: <span style="color:#a0a000"><http://xmlns.com/foaf/0.1/></span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">PREFIX</span> <span style="color:#00f;font-weight:bold">vCard</span>: <span style="color:#a0a000"><http://www.w3.org/2001/vcard-rdf/3.0#></span> |
| </span></span><span style="display:flex;"><span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#b8860b">?name</span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">WHERE</span> |
| </span></span><span style="display:flex;"><span>{ |
| </span></span><span style="display:flex;"><span> [] <span style="color:#b8860b">?p</span> <span style="color:#b8860b">?name</span> |
| </span></span><span style="display:flex;"><span> <span style="color:#a2f;font-weight:bold">FILTER</span> ( <span style="color:#b8860b">?p</span> <span style="color:#666">=</span> <span style="color:#00f;font-weight:bold">foaf</span>:<span style="color:#008000;font-weight:bold">name</span> <span style="color:#666">||</span> <span style="color:#b8860b">?p</span> <span style="color:#666">=</span> <span style="color:#00f;font-weight:bold">vCard</span>:<span style="color:#008000;font-weight:bold">FN</span> ) |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><p>testing whether the property is one URI or another. The solutions |
| may not come out in the same order. The first form is more likely |
| to be faster, depending on the data and the storage used, because |
| the second form may have to get all the triples from the graph to |
| match the triple pattern with unbound variables (or blank nodes) in |
| each slot, then test each <code>?p</code> to see if it matches one of the |
| values. It will depend on the sophistication of the query optimizer |
| as to whether it spots that it can perform the query more |
| efficiently and is able to pass the constraint down as well as to |
| the storage layer.</p> |
| <h2 id="union---remembering-where-the-data-was-found">UNION - remembering where the data was found.</h2> |
| <p>The example above used the same variable in each branch. If |
| different variables are used, the application can discover which |
| sub-pattern caused the match (<a href="sparql_data/q-union2.rq">q-union2.rq</a>):</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-sparql" data-lang="sparql"><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">PREFIX</span> <span style="color:#00f;font-weight:bold">foaf</span>: <span style="color:#a0a000"><http://xmlns.com/foaf/0.1/></span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">PREFIX</span> <span style="color:#00f;font-weight:bold">vCard</span>: <span style="color:#a0a000"><http://www.w3.org/2001/vcard-rdf/3.0#></span> |
| </span></span><span style="display:flex;"><span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#b8860b">?name1</span> <span style="color:#b8860b">?name2</span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">WHERE</span> |
| </span></span><span style="display:flex;"><span>{ |
| </span></span><span style="display:flex;"><span> { [] <span style="color:#00f;font-weight:bold">foaf</span>:<span style="color:#008000;font-weight:bold">name</span> <span style="color:#b8860b">?name1</span> } <span style="color:#a2f;font-weight:bold">UNION</span> { [] <span style="color:#00f;font-weight:bold">vCard</span>:<span style="color:#008000;font-weight:bold">FN</span> <span style="color:#b8860b">?name2</span> } |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-turtle" data-lang="turtle"><span style="display:flex;"><span><span style="">---------------------------------</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</span><span style="color:#bbb"> </span><span style="">nam</span><span style="color:#666">e1</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> </span><span style="">nam</span><span style="color:#666">e2</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">=================================</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</span><span style="color:#bbb"> </span><span style="color:#b44">"Matt Jones"</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</span><span style="color:#bbb"> </span><span style="color:#b44">"Sarah Jones"</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> </span><span style="color:#b44">"Becky Smith"</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</span><span style="color:#bbb"> </span><span style="">|</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></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">---------------------------------</span><span style="color:#bbb"> |
| </span></span></span></code></pre></div><p>This second query has retained information of where the name of the |
| person came from by assigning the name to different variables.</p> |
| <h2 id="optional-and-union">OPTIONAL and UNION</h2> |
| <p>In practice, <code>OPTIONAL</code> is more common than <code>UNION</code> but they both |
| have their uses. <code>OPTIONAL</code> are useful for augmenting the solutions |
| found, <code>UNION</code> is useful for concatenating the solutions from two |
| possibilities. They don’t necessary return the information in the |
| same way:</p> |
| <p>Query(<a href="sparql_data/q-union3.rq">q-union3.rq</a>):</p> |
| <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-sparql" data-lang="sparql"><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">PREFIX</span> <span style="color:#00f;font-weight:bold">foaf</span>: <span style="color:#a0a000"><http://xmlns.com/foaf/0.1/></span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">PREFIX</span> <span style="color:#00f;font-weight:bold">vCard</span>: <span style="color:#a0a000"><http://www.w3.org/2001/vcard-rdf/3.0#></span> |
| </span></span><span style="display:flex;"><span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">SELECT</span> <span style="color:#b8860b">?name1</span> <span style="color:#b8860b">?name2</span> |
| </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">WHERE</span> |
| </span></span><span style="display:flex;"><span>{ |
| </span></span><span style="display:flex;"><span> <span style="color:#b8860b">?x</span> <span style="color:#a2f;font-weight:bold">a</span> <span style="color:#00f;font-weight:bold">foaf</span>:<span style="color:#008000;font-weight:bold">Person</span> |
| </span></span><span style="display:flex;"><span> <span style="color:#a2f;font-weight:bold">OPTIONAL</span> { <span style="color:#b8860b">?x</span> <span style="color:#00f;font-weight:bold">foaf</span>:<span style="color:#008000;font-weight:bold">name</span> <span style="color:#b8860b">?name1</span> } |
| </span></span><span style="display:flex;"><span> <span style="color:#a2f;font-weight:bold">OPTIONAL</span> { <span style="color:#b8860b">?x</span> <span style="color:#00f;font-weight:bold">vCard</span>:<span style="color:#008000;font-weight:bold">FN</span> <span style="color:#b8860b">?name2</span> } |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-turtle" data-lang="turtle"><span style="display:flex;"><span><span style="">---------------------------------</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</span><span style="color:#bbb"> </span><span style="">nam</span><span style="color:#666">e1</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> </span><span style="">nam</span><span style="color:#666">e2</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">=================================</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</span><span style="color:#bbb"> </span><span style="color:#b44">"Matt Jones"</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</span><span style="color:#bbb"> </span><span style="color:#b44">"Sarah Jones"</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> </span><span style="color:#b44">"Becky Smith"</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> |
| </span></span></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">|</span><span style="color:#bbb"> </span><span style="">|</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></span><span style="display:flex;"><span><span style="color:#bbb"></span><span style="">---------------------------------</span><span style="color:#bbb"> |
| </span></span></span></code></pre></div><p>but beware of using <code>?name</code> in each <code>OPTIONAL</code> because that is an |
| order-dependent query.</p> |
| <p><a href="sparql_datasets.html">Next: Named Graphs</a></p> |
| |
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| <li><a href="#union---two-ways-to-the-same-data">UNION - two ways to the same data</a></li> |
| <li><a href="#union---remembering-where-the-data-was-found">UNION - remembering where the data was found.</a></li> |
| <li><a href="#optional-and-union">OPTIONAL and UNION</a></li> |
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