query: SELECT ?obra ?obraLabel ?museu ?museuLabel ?col ?colLabel
  WHERE {
    ?obra wdt:P276 ?museu.
    ?museu wdt:P31*/wdt:P279* wd:Q7328910.
    OPTIONAL {?obra wdt:P195 ?col}
  SERVICE wikibase:label {
  bd:serviceParam wikibase:language "[AUTO_LANGUAGE],ca,en" .
  ?museu rdfs:label ?museuLabel
  }
  SERVICE wikibase:label {
  bd:serviceParam wikibase:language "[AUTO_LANGUAGE],ca,en" .
  ?obra rdfs:label ?obraLabel
  }
  SERVICE wikibase:label {
  bd:serviceParam wikibase:language "[AUTO_LANGUAGE],ca,en" .
  ?col rdfs:label ?colLabel
  }
  }