SELECT DISTINCT COUNT(?uri) WHERE { ?x <http://dbpedia.org/ontology/author> <http://dbpedia.org/resource/Carl_Sagan> . ?x <http://dbpedia.org/property/subject> ?uri . }
Carl Sagan has penned books on how many matters?
SELECT DISTINCT COUNT ( ?z ) WHERE { ?g property:subject ?z . . ?g property:author resource:Carl_Sagan }
11
There are [11] subjects of the books authored by Carl Sagan.
Carl Sagan's books have [11] themes.
There are [11] subject of the books whose author is him .
There are [11] themes of books of which he is the author.
There are [11] subject of the books whose author is the person .
There are [11] subjects of books whose write is the person.