If you are not sure if a DGS instance provides a certain extension, just have a look at the metadata of the service, e.g. http://www.restful.ws/datagridservice/meta. You will find the all the available extensions with the predicate http://www.webcomposition.net/2008″02/dgs/meta/extension (we say “has extension”). In the example below we find the SA-REST extension I have introduced yesterday.

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:ns="http://purl.org/dc/elements/1.1/"
         xmlns:crud="http://www.webcomposition.net/2008/02/dgs/crud#"
         xmlns:meta="http://www.webcomposition.net/2008/02/dgs/meta/"
         xmlns:sarest="http://lsdis.cs.uga.edu/SAREST#">
  <rdf:Description rdf:about="http://www.restful.ws/DataGridService">
    <!-- ... -->
    <meta:extension>WebComposition.Dgs.Extensions.SaRest.SaRestHandler</meta:extension>
    <!-- ... -->
  </rdf:Description>
<rdf:RDF>