title: Japanese Virtuoso SPARQL EndPoint times out very quickly
body: <p>I am trying to use the following query on <a href="http://ja.dbpedia.org/sparql" rel="nofollow">Japanese dbpedia SPARQL Endpoint</a></p>
  
  <pre><code>select ?s  (group_concat(?album_ja ; separator = "|") AS ?name_album_ja_csv)  where{
     values ?sType { dbpedia-owl:Song
                         dbpedia-owl:Single
      } .
        ?s a ?sType .
        ?s (dbpedia-owl:album|^dbpedia-owl:album)* ?albums;rdfs:label ?album_ja      
      }group by ?s order by ?s offset 0 limit 10
  </code></pre>
  
  <p>but I get this error <strong>Virtuoso 42000 Error The estimated execution time 1005 (sec) exceeds the limit of 400 (sec).</strong>  Almost any query involving group by has this problem. Is this a server problem? Is my query inefficient? How can I get around it? </p>