Question: How many space missions have there been?
SPARQL query:
PREFIX res: <http://dbpedia.org/resource/>
PREFIX onto: <http://dbpedia.org/ontology/>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
SELECT COUNT(DISTINCT ?uri) WHERE 
{
	?uri rdf:type onto:SpaceMission .
}