Question: What is the subject of the book which preceded Sagan's Cosmos?
SPARQL query:
PREFIX prop: <http://dbpedia.org/property/>
PREFIX onto: <http://dbpedia.org/ontology/>
SELECT DISTINCT ?uri WHERE { <http://dbpedia.org/resource/Cosmos_(Carl_Sagan_book)> onto:previousWork ?x . ?x prop:subject ?uri  . }