Question: Do Prince Harry and Prince William have the same mother?
SPARQL:
PREFIX dbp: <http://dbpedia.org/property/>
ASK 
WHERE {       
        <http://dbpedia.org/resource/Prince_William,_Duke_of_Cambridge> dbp:mother ?x .  
	<http://dbpedia.org/resource/Prince_Harry_of_Wales> dbp:mother ?y . 
	FILTER (?x = ?y)
}