title: SPARQL Type Conversion?
body: <p>I have the following SPARQL query:</p>
  
  <pre><code>PREFIX ssn: &lt;http://purl.oclc.org/NET/ssnx/ssn#&gt; 
  PREFIX dtp: &lt;http://dtp-126.sncs.abdn.ac.uk#&gt; 
  PREFIX dbp: &lt;http://dbpedia.org/resource/&gt; 
  SELECT ?value ?time WHERE {         
      dtp:CD7514 ssn:madeObservation ?observation .       
      ?observation ssn:observedProperty ?property .   
      ?property ssn:hasValue &lt;http://dbpedia.org/resource/Temperature&gt; .          
      ?observation ssn:observationResult ?observationValue .      
      ?observationValue ssn:hasValue ?value .         
      ?observationValue ssn:observationSamplingTime ?time 
      FILTER(?time &gt; 1291908000)
  }
  </code></pre>
  
  <p>Which, in a nutshell, is selecting all temperature sensor observations from a sensor, dtp:CD7514, and filtering out values less than the given timestamp.</p>
  
  <p>However, adding the filter constraint returns 0 results (when there are observations that match this time region!)</p>
  
  <p>Is it possible that ?time is a varchar/text/String data type and therefore the comparison can't be done? If so, is it possible to do the conversion within SPARQL? </p>