Question: Who was the parent of person whose child is William C P breckinridge?
SPARQL:
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/property/children> <http://dbpedia.org/resource/William_Campbell_Preston_Breckinridge> . ?x <http://dbpedia.org/ontology/parent> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Person>}