Question: Was the wife of president Lincoln called Mary?
SPARQL query:
PREFIX onto: <http://dbpedia.org/ontology/>
PREFIX res: <http://dbpedia.org/resource/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
ASK 
WHERE {
        res:Abraham_Lincoln onto:spouse ?spouse .
        ?spouse rdfs:label ?name .
        FILTER(regex(?name,'Mary')) 
}