Question: What oldest structure does Donald Trump own?
Answer(s):
answer: Trump Tower

SPARQL query:
PREFIX ns: <http://rdf.freebase.com/ns/>
SELECT DISTINCT ?x
WHERE {
FILTER (?x != ns:m.0cqt90)
FILTER (!isLiteral(?x) OR lang(?x) = '' OR langMatches(lang(?x), 'en'))
ns:m.0cqt90 ns:architecture.architectural_structure_owner.structures_owned ?y .
?y ns:architecture.ownership.structure ?x .
FILTER(NOT EXISTS {?y ns:architecture.ownership.start_date ?sk0} || 
EXISTS {?y ns:architecture.ownership.start_date ?sk1 . 
FILTER(xsd:datetime(?sk1) <= "2015-08-10"^^xsd:dateTime) })
FILTER(NOT EXISTS {?y ns:architecture.ownership.end_date ?sk2} || 
EXISTS {?y ns:architecture.ownership.end_date ?sk3 . 
FILTER(xsd:datetime(?sk3) >= "2015-08-10"^^xsd:dateTime) })
?x ns:architecture.structure.opened ?num .
}
ORDER BY ?num LIMIT 1