Question: For which label did Elvis record his first album?
SPARQL query:
PREFIX onto: <http://dbpedia.org/ontology/>
PREFIX res: <http://dbpedia.org/resource/>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT DISTINCT ?uri ?string WHERE
{
	?x rdf:type onto:Album .
	?x onto:artist res:Elvis_Presley .
	?x onto:releaseDate ?y .
	?x onto:recordLabel ?uri .
	OPTIONAL { ?uri rdfs:label ?string. FILTER (lang(?string) = 'en') }
}
ORDER BY ASC(?y) LIMIT 1