Question: Carl Sagan has penned books on how many matters?
SPARQL query: SELECT DISTINCT COUNT(?uri) WHERE { ?x <http://dbpedia.org/ontology/author> <http://dbpedia.org/resource/Carl_Sagan> . ?x <http://dbpedia.org/property/subject> ?uri  . }
Answer: There are [11] subjects of the books authored by Carl Sagan.