Question: How many party leaders are there whose parties are headquartered in Berlin?
SPARQL query:
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX res: <http://dbpedia.org/resource/>
PREFIX onto: <http://dbpedia.org/ontology/>
SELECT DISTINCT COUNT(?uri) WHERE { ?x onto:headquarter <http://dbpedia.org/resource/Berlin> . ?x onto:leader ?uri . ?uri rdf:type onto:Politician}