Question: Who is the writer of the singles whose producer is Peter-John Vettese?
SPARQL:
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/property/producer> <http://dbpedia.org/resource/Peter-John_Vettese> . ?x <http://dbpedia.org/ontology/writer> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Single>}