query: #Properties grouped by their parent property
  #TODO: should display links and numeric ids
  #defaultView:Tree
  SELECT ?property2 ?property2Label ?property1 ?property1Label WHERE {
    ?property1 rdf:type wikibase:Property. #not replaceable with wikibase:Item, wikibase:Statement, wikibase:Reference at WDQS
                                           #https://www.mediawiki.org/wiki/Wikibase/Indexing/RDF_Dump_Format#WDQS_data_differences
    ?property1 wdt:P1647 ?property2.
    SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". }
  }