query: #title: Check prefix
  # Complex constraint from [[Property talk:P7149]]
  #
  SELECT ?item ?value ?prefix {
  	?item wdt:P7149 ?value.
      FILTER (REGEX(STR(?value), "^(.+/poi/.+)$")).
      BIND (STRBEFORE(STR(?value), "/poi/" ) AS ?prefix).
      FILTER NOT EXISTS { ?item0 wdt:P7149 ?prefix }
      FILTER (?prefix NOT IN ("all-parks"))
  }