Name the airlines which have a hub in airport in San Francisco?
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/property/cityServed> <http://dbpedia.org/resource/San_Francisco> . ?uri <http://dbpedia.org/property/hubs> ?x  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Airline>}
San_Francisco