query: SELECT ?item ?start ?end ?party ?ward
  WHERE 
  {
    ?item p:P39 ?ps .
    ?ps ps:P39 wd:Q55372701 .
    ?ps pq:P2715 wd:Q6515909 .
    OPTIONAL { ?ps pq:P4100 ?party . }
    OPTIONAL { ?ps pq:P768 ?ward . }
    OPTIONAL { ?ps pq:P580 ?start . }
    OPTIONAL { ?ps pq:P582 ?end . }
  }