title: Filter in SPARQL query
body: <p>I have the following SPARQL query:</p>
  
  <pre><code>PREFIX rdfs: &lt;http://www.w3.org/2000/01/rdf-schema#&gt; 
  PREFIX type: &lt;http://dbpedia.org/class/yago/&gt;      
  PREFIX prop: &lt;http://dbpedia.org/property/&gt;
  SELECT *
  WHERE {
    ?person a foaf:Person;
    foaf:name ?name;
    prop:deathCause ?death_cause.
    FILTER (langMatches(lang(?name), "EN")) .
  }
  LIMIT 50
  </code></pre>
  
  <p>If you run this here: <a href="http://dbpedia.org/snorql/" rel="nofollow">http://dbpedia.org/snorql/</a></p>
  
  <p>You will see that you get a lot of results. Now I would like to filter out one death cause, let's say 'Traffic collision'. So this should be simply by adding a filter:</p>
  
  <pre><code>FILTER (?death_cause = "Traffic collision").
  </code></pre>
  
  <p>So the query should then be:</p>
  
  <pre><code>PREFIX rdfs: &lt;http://www.w3.org/2000/01/rdf-schema#&gt; 
  PREFIX type: &lt;http://dbpedia.org/class/yago/&gt;      
  PREFIX prop: &lt;http://dbpedia.org/property/&gt;
  SELECT *
  WHERE {
    ?person a foaf:Person;
    foaf:name ?name;
    prop:deathCause ?death_cause.
    FILTER (?death_cause = "Traffic collision").
    FILTER (langMatches(lang(?name), "EN")) .
  }
  LIMIT 50
  </code></pre>
  
  <p>However this returns nothing. Anyone that knows what is wrong with the query? Thanks.</p>