title: SPARQL - Looking for all properties from particular namespace
body: <p>I am trying to determine the set of unique properties used in our DB from a particular namespace. For example, if I want to see all the properties we use from the Dublin Core set, I'm trying:</p>
  
  <pre><code>PREFIX rdf: &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#&gt;
  PREFIX rdfs: &lt;http://www.w3.org/2000/01/rdf-schema#&gt;
  PREFIX dc: &lt;http://purl.org/dc/elements/1.1/&gt;
  SELECT DISTINCT
      ?pred   
  WHERE 
      { 
      ?sub ?pred ?obj  . 
      FILTER regex(?pred, "purl.org/dc/elements") 
      } 
  limit 1000
  </code></pre>
  
  <p>I'm looking at all triples, filtering via regex for just triples with the DC namespace, and then returning a list of distinct predicates. This query times out when I run it, so I'm unsure if that's because of the volume being checked, or if the query itself is faulty.
  What I really want is a list of predicates that start with the DC namespace.</p>