How many artists have their works in the Sao Paolo Museum of Art?
SELECT DISTINCT COUNT(?uri) WHERE { ?x <http://dbpedia.org/property/museum> <http://dbpedia.org/resource/São_Paulo_Museum_of_Art> . ?x <http://dbpedia.org/property/artist> ?uri  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Artist>}
São_Paulo_Museum_of_Art