what is the {start time} for {Alexios I Komnenos} has {position held} as {Byzantine emperor} ?
When did Alexios I Kommenos become emperor of Byzatine?
When did Alexios I Komnenos become the Byzantine emperor?
SELECT ?p WHERE { ?b property:position_held resource:Byzantine_emperor . resource:Alexios_I_Komnenos property:position_held ?b . ?b property:start_time ?p }
select distinct ?value  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q41600> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P39> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> <http://wikidata.dbpedia.org/resource/Q18577504> .
?statement <http://www.wikidata.org/entity/P580> ?value. 
} 

SELECT ?value WHERE { wd:Q41600 p:P39 ?s . ?s ps:P39 wd:Q18577504 . ?s pq:P580 ?value}