Question: Which river's source place is Gloucestershire and mouth in North Sea?
SPARQL:
SELECT DISTINCT ?uri WHERE {?uri <http://dbpedia.org/ontology/sourcePlace> <http://dbpedia.org/resource/Gloucestershire> . ?uri <http://dbpedia.org/ontology/riverMouth> <http://dbpedia.org/resource/North_Sea>  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/River>}