Question: Who wrote the lyrics for the Polish national anthem?
SPARQL query:
PREFIX onto: <http://dbpedia.org/ontology/>
PREFIX prop: <http://dbpedia.org/property/>
PREFIX res: <http://dbpedia.org/resource/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT DISTINCT ?uri ?string WHERE
{
	res:Poland onto:anthem ?x .
        ?x prop:author ?uri .
	OPTIONAL { ?uri rdfs:label ?string. FILTER (lang(?string) = 'en') }
}