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