Question: Which capitals in Europe were host cities of the summer olympic games?
SPARQL:
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX yago: <http://dbpedia.org/class/yago/>
SELECT ?uri ?string
WHERE 
{
	?uri rdf:type yago:CapitalsInEurope .
        ?uri rdf:type yago:HostCitiesOfTheSummerOlympicGames .
        OPTIONAL {?uri rdfs:label ?string . FILTER (lang(?string) = 'en') } 
}