What are the airlines whose hub is San Francisco International Airport?
SELECT DISTINCT ?uri WHERE {?uri <http://dbpedia.org/property/hubs> <http://dbpedia.org/resource/San_Francisco_International_Airport>  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Airline>}
San_Francisco_International_Airport