Question: Name the river with mouth palce Essex and source place as Gloucestershire ?
SPARQL:
SELECT DISTINCT ?uri WHERE {?uri <http://dbpedia.org/ontology/mouthPlace> <http://dbpedia.org/resource/Essex> . ?uri <http://dbpedia.org/ontology/sourcePlace> <http://dbpedia.org/resource/Gloucestershire>  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/River>}