title: Determine if a specific triple exists using SPARQL
body: <p>If the data set is:</p>
  
  <pre><code>@prefix dc:   &lt;http://purl.org/dc/elements/1.1/&gt; .
  @prefix :     &lt;http://example.org/book/&gt; .
  @prefix ns:   &lt;http://example.org/ns#&gt; .
  
  :book1  dc:title  "SPARQL Tutorial" .
  :book2  dc:title  "The Semantic Web" .
  </code></pre>
  
  <p>How do I check that the triple <code>:book1  dc:title  "SPARQL Tutorial" .</code> exists?</p>
  
  <p>I can do <code>SELECT ?book where {?book dc:title "SPARQL Tutorial"}</code> but then I have to do post processing to determine if 'book1' was retrieved!</p>