query: #title: Tags using keys that have no entity
  # Complex constraint from [[Property talk:P1282]]
  # Extracts "key" from "Tag:key=value" if there is no "Key:key"
  SELECT (SAMPLE(?item) as ?item) ?key (COUNT(DISTINCT ?tag) as ?ct) (GROUP_CONCAT(DISTINCT ?tag; separator=" ; ") as ?tags)
  WITH
  {  SELECT * WHERE
    {
  	?item p:P1282/ps:P1282 ?osm2 .
      FILTER(CONTAINS(str(?osm2), "Tag:"))
      BIND(strafter(str(?osm2), "Tag:") as ?tag)
      BIND(CONCAT("Key:",strbefore(str(?tag), "=")) as ?key)
    }
  } as %tags
  WHERE
  { 
     INCLUDE %tags
     FILTER NOT EXISTS { [] wdt:P1282 ?key }         
  }
  GROUP BY ?key
  ORDER BY DESC(?ct)