Question: What non fiction subjects are covered in books by Doubleday publishers?
SPARQL query:
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX res: <http://dbpedia.org/resource/>
PREFIX onto: <http://dbpedia.org/ontology/>
SELECT DISTINCT ?uri WHERE { ?x onto:publisher <http://dbpedia.org/resource/Doubleday_(publisher)> . ?x onto:nonFictionSubject ?uri . ?x rdf:type onto:Book}