Question: From how many countries have people participated in the Excelsior Stakes?
SPARQL query:
PREFIX res: <http://dbpedia.org/resource/>
PREFIX prop: <http://dbpedia.org/property/>
PREFIX onto: <http://dbpedia.org/ontology/>
SELECT DISTINCT COUNT(?uri) WHERE { ?x prop:race <http://dbpedia.org/resource/Excelsior_Stakes> . ?x onto:birthPlace ?uri . }