Question: Who is the mayor of New York City?
SPARQL query:
PREFIX res: <http://dbpedia.org/resource/>
PREFIX onto: <http://dbpedia.org/ontology/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT ?uri ?string
WHERE
{ 
        res:New_York_City onto:leaderName ?uri .
        OPTIONAL {?uri rdfs:label ?string. FILTER (lang(?string) = 'en') }
}