A query is composed of an RDF dataset, or references to the graph or graphs against which the query will be executed; and the query itself -- in this case, the query is a string conforming to a grammar @@. @@ quote the spec... An rdf-dataset is a set of URIs, zero or one of which is the default graph (which might also be called the anonymous graph, since it cannot be named); and zero or any number of named graphs. The type for serializaing query results, either as VBR XML or RDF/XML.