title: SPARQL query in dotnetrdf does not query imported ontology
body: <p>What I am trying to do is list all the classes using the following query in an owl file which I created using Protege 5 and has "foaf" as imported ontology.</p>
  
  <pre><code>PREFIX rdf: &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#&gt;
  PREFIX owl: &lt;http://www.w3.org/2002/07/owl#&gt;
  PREFIX rdfs: &lt;http://www.w3.org/2000/01/rdf-schema#&gt;
  PREFIX xsd: &lt;http://www.w3.org/2001/XMLSchema#&gt;
  SELECT DISTINCT ?subject ?label ?comment
      WHERE 
      { 
          ?subject a owl:Class 
          OPTIONAL { ?subject a rdfs:Class }
          OPTIONAL { ?subject rdfs:label ?label }
          OPTIONAL { ?subject rdfs:comment ?comment}
      }
  </code></pre>
  
  <p>Problem is, when I run this query in SPARQL tab of Protege I get all the classes defined in "foaf" namespace but when I try to run the same query using dotnetrdf api in c# I don't get the same result.</p>
  
  <p>Following is my code in c#</p>
  
  <pre><code>var g = new Graph();
  g.LoadFromFile(owlFile, new TurtleParser());
  ISparqlDataset ds = new InMemoryDataset(g);
  LeviathanQueryProcessor processor = new LeviathanQueryProcessor(ds);
  var queryParser = new SparqlQueryParser();
  var parmeterizedString = new SparqlParameterizedString(query);
  parmeterizedString.SetLiteral("value", searchQuery);
  return processor.ProcessQuery(queryParser.ParseFromString(parmeterizedString.ToString())) as SparqlResultSet;
  </code></pre>
  
  <p>What am i doing wrong ?</p>