怎么在C#中执行spatql？

Question

怎么在C#中执行spatql？
我下面的代码执行的时候总是提示错误
public void GetGraphFromDB()
        {
            SemanticServerStorage db = new SemanticServerStorage(
                _connectionString,
                _graphURI, 
                @"PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
                  PREFIX rdf:   <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
                  CONSTRUCT   {?s rdfs:label ?name}
                  FROM <http://www.intellidimension.com/resources/samples/RoundTrip>
                  WHERE {?s rdf:type rdfs:Class; rdfs:label ?name}");            _graph = new GraphDataSource();
            db.Load(_graph);            StringWriter s = new StringWriter();
            _graph.Format<NTriplesFormatter>(s);            Console.Write("Graph retrieved from DB\n:" + s);
        }
错误信息是： Expected command