Question: During the time, the singer who created the song "Happy Birthday, Mr. President" was killed, who was the President?
Answer(s):
answer: Lyndon B. Johnson

SPARQL query:
PREFIX ns: <http://rdf.freebase.com/ns/>
SELECT DISTINCT ?x
WHERE {
FILTER (?x != ?c)
FILTER (!isLiteral(?x) OR lang(?x) = '' OR langMatches(lang(?x), 'en'))
?c ns:music.featured_artist.recordings ns:m.0_jd323 . 
?c ns:government.us_president.vice_president ?x .
}