Question: Give me all films produced by Hal Roach.
SPARQL:
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX onto: <http://dbpedia.org/ontology/>
SELECT DISTINCT ?uri ?string
WHERE 
{
	?uri rdf:type onto:Film .
        ?uri onto:producer ?producer .
        ?producer rdfs:label 'Hal Roach'@en .
	OPTIONAL {?uri rdfs:label ?string . FILTER (lang(?string) = 'en') }
}