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             <h1 class="title">ARQ - Negation</h1>

 	<h3 id="negation-by-failure-optional--bound">Negation by Failure (OPTIONAL + !BOUND)</h3>
 <p>Standard SPARQL 1.0 can perform negation using the idiom of
 <code>OPTIONAL</code>/<code>!BOUND</code>. It is inconvenient and can be hard to use as
 complexity increases. SPARQL 1.1 supports additional operators for
 negation.</p>
 <pre><code># Names of people who have not stated that they know anyone
 PREFIX foaf: &lt;http://xmlns.com/foaf/0.1/&gt;
 SELECT ?name
 WHERE
 {
   ?x foaf:givenName  ?name .
   OPTIONAL { ?x foaf:knows ?who } .
   FILTER (!BOUND(?who))
 }
 </code></pre>
 <h3 id="exists-and-not-exists">EXISTS and NOT EXISTS</h3>
 <p>The <code>EXISTS</code> and <code>NOT EXISTS</code> are now legal SPARQL 1.1 when used inside a <code>FILTER</code>,
 they may be used as bare graph patterns only when <code>Syntax.syntaxARQ</code> is used</p>
 <p>There is the <code>NOT EXISTS</code> operator which acts at the point in the query where it is
 written. It does not bind any variables but variables already bound
 in the query will have their bound value.</p>
 <pre><code># Names of people who have not stated that they know anyone
 PREFIX foaf: &lt;http://xmlns.com/foaf/0.1/&gt;
 SELECT ?name
 WHERE
 {
   ?x foaf:givenName ?name .
   FILTER NOT EXISTS { ?x foaf:knows ?who }
 }
 </code></pre>
 <p>There is also an <code>EXISTS</code> operator.</p>
 <pre><code># Names of people where it is stated that they know at least one other person.
 PREFIX foaf: &lt;http://xmlns.com/foaf/0.1/&gt;
 SELECT ?name
 WHERE
 {
   ?x foaf:givenName ?name .
   FILTER EXISTS { ?x foaf:knows ?who . FILTER(?who != ?x) }
 }
 </code></pre>
 <p>In this example, the pattern is a little more complex. Any graph
 pattern is allowed although use of <code>OPTIONAL</code> is pointless (which
 will always match, possible with no additional results).</p>
 <p><code>NOT EXISTS</code> and <code>EXISTS</code> can also be used in <code>FILTER</code> expressions.
 In SPARQL, <code>FILTER</code> expressions act over the whole of the basic
 graph pattern in which they occur.</p>
 <pre><code># Names of people who have not stated that they know anyone
 PREFIX foaf: &lt;http://xmlns.com/foaf/0.1/&gt;
 SELECT ?name
 WHERE
 {
   ?x foaf:givenName ?name .
   FILTER (NOT EXISTS { ?x foaf:knows ?who })
  }
 </code></pre>
 <p>A note of caution:</p>
 <pre><code>PREFIX foaf: &lt;http://xmlns.com/foaf/0.1/&gt;
 SELECT ?name
 WHERE
 {
   ?x foaf:givenName ?name .
   FILTER (NOT EXISTS { ?x foaf:knows ?y })
   ?x foaf:knows ?who
 }
 </code></pre>
 <p>is the same as (it&rsquo;s a single basic graph pattern - the filter does
 not break it in two):</p>
 <pre><code>PREFIX foaf: &lt;http://xmlns.com/foaf/0.1/&gt;
 SELECT ?name
 WHERE
 {
   ?x foaf:givenName ?name .
   ?x foaf:knows ?y .
   FILTER (NOT EXISTS { ?x foaf:knows ?who })
 }
 </code></pre>
 <p>and the <code>FILTER</code> will always be false (<code>{ ?x foaf:knows ?y }</code> must
 have matched to get to this point in the query and using <code>?who</code>
 instead makes no difference).</p>
 <h3 id="minus">MINUS</h3>
 <p>SPARQL 1.1 also provides a <code>MINUS</code> keyword which is broadly similar to
 <code>NOT EXISTS</code> though does have some key differences as explained in the <a href="http://www.w3.org/TR/sparql11-query/#neg-notexists-minus">specification</a>:</p>
 <pre><code>PREFIX foaf: &lt;http://xmlns.com/foaf/0.1/&gt;
 SELECT ?name
 WHERE
 {
   ?x foaf:givenName ?name .
   ?x foaf:knows ?y .
   MINUS { ?x foaf:knows &lt;http://example.org/A&gt; }
 }
 </code></pre>
 <p>Here we subtract any solutions where <code>?x</code> also knows <code>http://example.org/A</code></p>
 <p>One of the key differences between <code>MINUS</code> and <code>NOT EXISTS</code> is that it is a child graph pattern and so breaks
 the graph pattern and so the result of the query can change depending where the <code>MINUS</code> is placed.  This is
 unlike the earlier <code>NOT EXISTS</code> examples where moving the position of the <code>FILTER</code> resulted
 in equivalent queries.</p>
 <h3 id="not-in">NOT IN</h3>
 <p>SPARQL 1.1 also has a simpler form of negation for when you simply
 need to restrict a variable to not being in a given set of values, this is the
 <code>NOT IN</code> function:</p>
 <pre><code>PREFIX foaf: &lt;http://xmlns.com/foaf/0.1/&gt;
 SELECT ?name
 WHERE
 {
   ?x foaf:givenName ?name .
   ?x foaf:knows ?y .
   FILTER(?y NOT IN (&lt;http://example.org/A&gt;, &lt;http://example.org/B&gt;))
 }
 </code></pre>
 <p>This would filter out matches where the value of <code>?y</code> is either <code>http://example.org/A</code> or <code>http://example.org/B</code></p>
 <p><a href="index.html">ARQ documentation index</a></p>


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	</div>
	<h1 class="title">ARQ - Negation</h1>

	<h3 id="negation-by-failure-optional--bound">Negation by Failure (OPTIONAL + !BOUND)</h3>
	<p>Standard SPARQL 1.0 can perform negation using the idiom of
	<code>OPTIONAL</code>/<code>!BOUND</code>. It is inconvenient and can be hard to use as
	complexity increases. SPARQL 1.1 supports additional operators for
	negation.</p>
	<pre><code># Names of people who have not stated that they know anyone
	PREFIX foaf: <http://xmlns.com/foaf/0.1/>
	SELECT ?name
	WHERE
	{
	?x foaf:givenName ?name .
	OPTIONAL { ?x foaf:knows ?who } .
	FILTER (!BOUND(?who))
	}
	</code></pre>
	<h3 id="exists-and-not-exists">EXISTS and NOT EXISTS</h3>
	<p>The <code>EXISTS</code> and <code>NOT EXISTS</code> are now legal SPARQL 1.1 when used inside a <code>FILTER</code>,
	they may be used as bare graph patterns only when <code>Syntax.syntaxARQ</code> is used</p>
	<p>There is the <code>NOT EXISTS</code> operator which acts at the point in the query where it is
	written. It does not bind any variables but variables already bound
	in the query will have their bound value.</p>
	<pre><code># Names of people who have not stated that they know anyone
	PREFIX foaf: <http://xmlns.com/foaf/0.1/>
	SELECT ?name
	WHERE
	{
	?x foaf:givenName ?name .
	FILTER NOT EXISTS { ?x foaf:knows ?who }
	}
	</code></pre>
	<p>There is also an <code>EXISTS</code> operator.</p>
	<pre><code># Names of people where it is stated that they know at least one other person.
	PREFIX foaf: <http://xmlns.com/foaf/0.1/>
	SELECT ?name
	WHERE
	{
	?x foaf:givenName ?name .
	FILTER EXISTS { ?x foaf:knows ?who . FILTER(?who != ?x) }
	}
	</code></pre>
	<p>In this example, the pattern is a little more complex. Any graph
	pattern is allowed although use of <code>OPTIONAL</code> is pointless (which
	will always match, possible with no additional results).</p>
	<p><code>NOT EXISTS</code> and <code>EXISTS</code> can also be used in <code>FILTER</code> expressions.
	In SPARQL, <code>FILTER</code> expressions act over the whole of the basic
	graph pattern in which they occur.</p>
	<pre><code># Names of people who have not stated that they know anyone
	PREFIX foaf: <http://xmlns.com/foaf/0.1/>
	SELECT ?name
	WHERE
	{
	?x foaf:givenName ?name .
	FILTER (NOT EXISTS { ?x foaf:knows ?who })
	}
	</code></pre>
	<p>A note of caution:</p>
	<pre><code>PREFIX foaf: <http://xmlns.com/foaf/0.1/>
	SELECT ?name
	WHERE
	{
	?x foaf:givenName ?name .
	FILTER (NOT EXISTS { ?x foaf:knows ?y })
	?x foaf:knows ?who
	}
	</code></pre>
	<p>is the same as (it’s a single basic graph pattern - the filter does
	not break it in two):</p>
	<pre><code>PREFIX foaf: <http://xmlns.com/foaf/0.1/>
	SELECT ?name
	WHERE
	{
	?x foaf:givenName ?name .
	?x foaf:knows ?y .
	FILTER (NOT EXISTS { ?x foaf:knows ?who })
	}
	</code></pre>
	<p>and the <code>FILTER</code> will always be false (<code>{ ?x foaf:knows ?y }</code> must
	have matched to get to this point in the query and using <code>?who</code>
	instead makes no difference).</p>
	<h3 id="minus">MINUS</h3>
	<p>SPARQL 1.1 also provides a <code>MINUS</code> keyword which is broadly similar to
	<code>NOT EXISTS</code> though does have some key differences as explained in the <a href="http://www.w3.org/TR/sparql11-query/#neg-notexists-minus">specification</a>:</p>
	<pre><code>PREFIX foaf: <http://xmlns.com/foaf/0.1/>
	SELECT ?name
	WHERE
	{
	?x foaf:givenName ?name .
	?x foaf:knows ?y .
	MINUS { ?x foaf:knows <http://example.org/A> }
	}
	</code></pre>
	<p>Here we subtract any solutions where <code>?x</code> also knows <code>http://example.org/A</code></p>
	<p>One of the key differences between <code>MINUS</code> and <code>NOT EXISTS</code> is that it is a child graph pattern and so breaks
	the graph pattern and so the result of the query can change depending where the <code>MINUS</code> is placed. This is
	unlike the earlier <code>NOT EXISTS</code> examples where moving the position of the <code>FILTER</code> resulted
	in equivalent queries.</p>
	<h3 id="not-in">NOT IN</h3>
	<p>SPARQL 1.1 also has a simpler form of negation for when you simply
	need to restrict a variable to not being in a given set of values, this is the
	<code>NOT IN</code> function:</p>
	<pre><code>PREFIX foaf: <http://xmlns.com/foaf/0.1/>
	SELECT ?name
	WHERE
	{
	?x foaf:givenName ?name .
	?x foaf:knows ?y .
	FILTER(?y NOT IN (<http://example.org/A>, <http://example.org/B>))
	}
	</code></pre>
	<p>This would filter out matches where the value of <code>?y</code> is either <code>http://example.org/A</code> or <code>http://example.org/B</code></p>
	<p><a href="index.html">ARQ documentation index</a></p>


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