Question: Which birds are there in the United States?
SPARQL:
PREFIX yago: <http://dbpedia.org/class/yago/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
SELECT DISTINCT ?uri ?string
WHERE 
{
	?uri rdf:type yago:BirdsOfTheUnitedStates.
        OPTIONAL {?uri rdfs:label ?string . FILTER (lang(?string) = 'en') }
}