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| <h1 class="title">SPARQL Tutorial - Optional Information</h1> |
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| <main class="d-flex flex-xl-row flex-column"> |
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| <h2 class="h6 sticky-top m-0 p-2 bg-body-tertiary">On this page</h2> |
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| <ul> |
| <li><a href="#optionals">OPTIONALs</a></li> |
| <li><a href="#optionals-with-filters">OPTIONALs with FILTERs</a></li> |
| <li><a href="#optionals-and-order-dependent-queries">OPTIONALs and Order Dependent Queries</a></li> |
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| <article class="flex-column me-lg-4"> |
| <p>RDF is semi-structured data so SPARQL has a the ability to query |
| for data but not to fail query when that data does not exist. The |
| query is using an optional part to extend the information found in |
| a query solution but to return the non-optional information |
| anyway.</p> |
| <h2 id="optionals">OPTIONALs</h2> |
| <p>This query (<a href="sparql_data/q-opt1.rq">q-opt1.rq</a>) gets the name of a person and |
| also their age if that piece of information is available.</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">info</span>: <span style="color:#a0a000"><http://somewhere/peopleInfo#></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 style="color:#b8860b">?age</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">?person</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 style="color:#a2f;font-weight:bold">OPTIONAL</span> { <span style="color:#b8860b">?person</span> <span style="color:#00f;font-weight:bold">info</span>:<span style="color:#008000;font-weight:bold">age</span> <span style="color:#b8860b">?age</span> } |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><p>Two of the four people in the data (<a href="sparql_data/vc-db-2.rdf">vc-db-2.rdf</a>)have |
| age properties so two of the query solutions have that |
| information. However, because the triple pattern for the age is |
| optional, there is a pattern solution for the people who don’t have |
| age information.</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 style="">age</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">"Becky Smith"</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> </span><span style="color:#666">23</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="color:#b44">"John Smith"</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> </span><span style="color:#666">25</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></span></code></pre></div><p>If the optional clause had not been there, no age information would |
| have been retrieved. If the triple pattern had been included but |
| not optional then we would have the query |
| (<a href="sparql_data/q-opt2.rq">q-opt2.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">info</span>: <span style="color:#a0a000"><http://somewhere/peopleInfo#></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 style="color:#b8860b">?age</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">?person</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 style="color:#b8860b">?person</span> <span style="color:#00f;font-weight:bold">info</span>:<span style="color:#008000;font-weight:bold">age</span> <span style="color:#b8860b">?age</span> . |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><p>with only two solutions:</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 style="">age</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">"Becky Smith"</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> </span><span style="color:#666">23</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 style="color:#666">25</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>because the <code>info:age</code> property must now be present in a solution.</p> |
| <h2 id="optionals-with-filters">OPTIONALs with FILTERs</h2> |
| <p><code>OPTIONAL</code> is a binary operator that combines two graph patterns. |
| The optional pattern is any group pattern and may involve any |
| SPARQL pattern types. If the group matches, the solution is |
| extended, if not, the original solution is given |
| (<a href="sparql_data/q-opt3.rq">q-opt3.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">info</span>: <span style="color:#a0a000"><http://somewhere/peopleInfo#></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 style="color:#b8860b">?age</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">?person</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 style="color:#a2f;font-weight:bold">OPTIONAL</span> { <span style="color:#b8860b">?person</span> <span style="color:#00f;font-weight:bold">info</span>:<span style="color:#008000;font-weight:bold">age</span> <span style="color:#b8860b">?age</span> . <span style="color:#a2f;font-weight:bold">FILTER</span> ( <span style="color:#b8860b">?age</span> <span style="color:#666">></span> <span style="color:#666">24</span> ) } |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><p>So, if we filter for ages greater than 24 in the optional part, we |
| will still get 4 solutions (from the <code>vcard:FN</code> pattern) but only |
| get ages if they pass the test.</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 style="">age</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">"Becky Smith"</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="color:#b44">"John Smith"</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> </span><span style="color:#666">25</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></span></code></pre></div><p>No age included for “Becky Smith” because it is less than 24.</p> |
| <p>If the filter condition is moved out of the optional part, then it |
| can influence the number of solutions, but it may be necessary to |
| make the filter more complicated to allow for variable <code>age</code> being |
| unbound (<a href="sparql_data/q-opt4.rq">q-opt4.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">info</span>: <span style="color:#a0a000"><http://somewhere/peopleInfo#></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 style="color:#b8860b">?age</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">?person</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 style="color:#a2f;font-weight:bold">OPTIONAL</span> { <span style="color:#b8860b">?person</span> <span style="color:#00f;font-weight:bold">info</span>:<span style="color:#008000;font-weight:bold">age</span> <span style="color:#b8860b">?age</span> . } |
| </span></span><span style="display:flex;"><span> <span style="color:#a2f;font-weight:bold">FILTER</span> ( <span style="color:#666">!</span><span style="color:#00a000">bound</span>(<span style="color:#b8860b">?age</span>) <span style="color:#666">||</span> <span style="color:#b8860b">?age</span> <span style="color:#666">></span> <span style="color:#666">24</span> ) |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><p>If a solution has an <code>age</code> variable, then it must be greater than |
| 24. It can also be unbound. There are now three solutions:</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 style="">age</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">"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="color:#b44">"John Smith"</span><span style="color:#bbb"> </span><span style="">|</span><span style="color:#bbb"> </span><span style="color:#666">25</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></span></code></pre></div><p>Evaluating an expression which has an unbound variables where a |
| bound one was expected causes an evaluation exception and the whole |
| expression fails.</p> |
| <h2 id="optionals-and-order-dependent-queries">OPTIONALs and Order Dependent Queries</h2> |
| <p>One thing to be careful of is using the same variable in two or |
| more optional clauses (and not in some basic pattern as well):</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">?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">?name</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">?name</span> } |
| </span></span><span style="display:flex;"><span>} |
| </span></span></code></pre></div><p>If the first optional binds <code>?name</code> and <code>?x</code> to some values, the |
| second <code>OPTIONAL</code> is an attempt to match the ground triples (<code>?x</code> |
| and <code>?name</code> have values). If the first optional did not |
| match the optional part, then the second one is an attempt to match |
| its triple with two variables.</p> |
| <p>With an example set of data in which every combination of values exist:</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-xml" data-lang="xml"><span style="display:flex;"><span><span style="color:#008000;font-weight:bold"><rdf:RDF</span> |
| </span></span><span style="display:flex;"><span> <span style="color:#b44">xmlns:rdf=</span><span style="color:#b44">'http://www.w3.org/1999/02/22-rdf-syntax-ns#'</span> |
| </span></span><span style="display:flex;"><span> <span style="color:#b44">xmlns:vCard=</span><span style="color:#b44">'http://www.w3.org/2001/vcard-rdf/3.0#'</span> |
| </span></span><span style="display:flex;"><span> <span style="color:#b44">xmlns:info=</span><span style="color:#b44">'http://somewhere/peopleInfo#'</span> |
| </span></span><span style="display:flex;"><span> <span style="color:#b44">xmlns:foaf=</span><span style="color:#b44">'http://xmlns.com/foaf/0.1/'</span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold">></span> |
| </span></span><span style="display:flex;"><span> |
| </span></span><span style="display:flex;"><span> <span style="color:#080;font-style:italic"><!-- both vCard:FN and foaf:name have values, and the values are the same --></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"><foaf:Person</span> <span style="color:#b44">rdf:about=</span><span style="color:#b44">"http://somewhere/JohnSmith"</span><span style="color:#008000;font-weight:bold">></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"><vCard:FN></span>John Smith<span style="color:#008000;font-weight:bold"></vCard:FN></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"><foaf:name></span>John Smith<span style="color:#008000;font-weight:bold"></foaf:name></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"></foaf:Person></span> |
| </span></span><span style="display:flex;"><span> |
| </span></span><span style="display:flex;"><span> <span style="color:#080;font-style:italic"><!-- both vCard:FN and foaf:name have values, but the values are not the same --></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"><foaf:Person</span> <span style="color:#b44">rdf:about=</span><span style="color:#b44">"http://somewhere/RebeccaSmith"</span><span style="color:#008000;font-weight:bold">></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"><vCard:FN></span>Becky Smith<span style="color:#008000;font-weight:bold"></vCard:FN></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"><foaf:name></span>Rebecca Smith<span style="color:#008000;font-weight:bold"></foaf:name></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"></foaf:Person></span> |
| </span></span><span style="display:flex;"><span> |
| </span></span><span style="display:flex;"><span> <span style="color:#080;font-style:italic"><!-- only vCard:FN has values --></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"><foaf:Person</span> <span style="color:#b44">rdf:about=</span><span style="color:#b44">"http://somewhere/SarahJones"</span><span style="color:#008000;font-weight:bold">></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"><vCard:FN></span>Sarah Jones<span style="color:#008000;font-weight:bold"></vCard:FN></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"></foaf:Person></span> |
| </span></span><span style="display:flex;"><span> |
| </span></span><span style="display:flex;"><span> <span style="color:#080;font-style:italic"><!-- only foaf:name has values --></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"><foaf:Person</span> <span style="color:#b44">rdf:about=</span><span style="color:#b44">"http://somewhere/MattJones"</span><span style="color:#008000;font-weight:bold">></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"><foaf:name></span>Matthew Jones<span style="color:#008000;font-weight:bold"></foaf:name></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"></foaf:Person></span> |
| </span></span><span style="display:flex;"><span> |
| </span></span><span style="display:flex;"><span> <span style="color:#080;font-style:italic"><!-- neither vCard:FN nor foaf:name have values --></span> |
| </span></span><span style="display:flex;"><span> <span style="color:#008000;font-weight:bold"><foaf:Person</span> <span style="color:#b44">rdf:about=</span><span style="color:#b44">"http://somewhere/AdamJones"</span> <span style="color:#008000;font-weight:bold">/></span> |
| </span></span><span style="display:flex;"><span> |
| </span></span><span style="display:flex;"><span><span style="color:#008000;font-weight:bold"></rdf:RDF></span> |
| </span></span></code></pre></div><p>Executing the above query will yield these solutions:</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">"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 style="color:#b44">"Matthew 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="">|</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">"Rebecca 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><a href="sparql_union.html">Next: union queries</a></p> |
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