Question: Which airports are located in California, USA?
SPARQL:
PREFIX dbo: <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 { 
	?uri rdf:type dbo:Airport .
        ?uri dbo:location res:California .
        OPTIONAL { ?uri rdfs:label ?string . FILTER (lang(?string) = 'en') }
}