what is the {start time} for {Selena Gomez} has {partner} as {Justin Bieber} ?
When did Justin Bieber and Selena Gomez get together romantically?
When did Selena Gomez become romantically involved with Justin Bieber?
SELECT ?d WHERE { resource:Selena_Gomez property:unmarried_partner ?q . ?q property:start_time ?d . ?q property:unmarried_partner resource:Justin_Bieber }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q83287> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P451> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> <http://wikidata.dbpedia.org/resource/Q34086> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q83287 p:P451 ?s . ?s ps:P451 wd:Q34086 . ?s pq:P580 ?value}