what is the {start time} for {Marie Louise, Duchess of Parma} has {spouse} as {Napoleon} ?
When was Napoleon married to Marie Louise, Duchess of Parma?
When was Marie Louise, Duchess of Parma the spouse of Napoleon ?
SELECT ?p WHERE { ?k property:spouse resource:Napoleon . ?k property:start_time ?p . resource:Marie_Louise,_Duchess_of_Parma property:spouse ?k }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q157491> .
?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/Q517> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q157491 p:P26 ?s . ?s ps:P26 wd:Q517 . ?s pq:P580 ?value}