Question: List all the operators of the train who operates in Budapest ?
SPARQL:
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/operator> <http://dbpedia.org/resource/Budapest> . ?x <http://dbpedia.org/ontology/operator> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Train>}