Question: In how many countries do the rivers start which end at the Caspian Sea?
SPARQL query:
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX onto: <http://dbpedia.org/ontology/>
SELECT DISTINCT COUNT(?uri) WHERE { ?x onto:riverMouth <http://dbpedia.org/resource/Caspian_Sea> . ?x onto:sourceCountry ?uri  . ?uri rdf:type onto:Country}