Project(Service(<https://localhost/bobdc/beatles-musicians/sparql>,
                Project(BGP( ?song <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://learningsparql.com/ns/schema/Song> .
                             ?song <http://www.w3.org/2000/01/rdf-schema#label> 'The Long And Winding Road' .
                             ?song <http://learningsparql.com/ns/instrument/bass> ?bassist),
                        {?bassist}), true),
        {?bassist})