what is the {start time} for {Incheon} has {head of government} as {Song Young-gil} ?
What date did the head of the government of Incheon change to Song Young-gil?
When did Song Young-gil become head of the government of Incheon?
SELECT ?y WHERE { ?q property:head_of_government resource:Song_Young-gil . resource:Incheon property:head_of_government ?q . ?q property:start_time ?y }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q20934> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P6> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> <http://wikidata.dbpedia.org/resource/Q484024> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q20934 p:P6 ?s . ?s ps:P6 wd:Q484024 . ?s pq:P580 ?value}