what is the {start time} for {Deng Xiaoping} has {spouse} as {Zhang Xiyuan} ?
What date were Deng Xiaoping marry Zhang Xiyuan?
When did Deng Xiaoping marry Zhang Xiyuan?
SELECT ?v WHERE { resource:Deng_Xiaoping property:spouse ?v . ?v property:start_time ?v . ?v property:spouse resource:Zhang_Xiyuan }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q16977> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P26> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> <http://wikidata.dbpedia.org/resource/Q4121474> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q16977 p:P26 ?s . ?s ps:P26 wd:Q4121474 . ?s pq:P580 ?value}