Question: How many non-fiction subject are there of the books whose one of the non-fiction subject is Ankh-Morpork City Watch ?
SPARQL query:
PREFIX onto: <http://dbpedia.org/ontology/>
 SELECT DISTINCT COUNT(?uri) WHERE { ?x onto:nonFictionSubject <http://dbpedia.org/resource/Ankh-Morpork_City_Watch> . ?x onto:nonFictionSubject ?uri }