code: def mainset(self):
          
          if self.mainsetcache:
              return self.mainsetcache
          set_uri = self.get_set_uri()
          for row in self.graph.query("SELECT ?seturi ?setid ?setlabel ?setopen ?setempty WHERE { ?seturi rdf:type skos:Collection . OPTIONAL { ?seturi skos:notation ?setid } OPTIONAL { ?seturi skos:prefLabel ?setlabel } OPTIONAL { ?seturi fsd:open ?setopen } OPTIONAL { ?seturi fsd:empty ?setempty } FILTER NOT EXISTS { ?y skos:member ?seturi . ?y rdf:type skos:Collection } }"):
              self.mainsetcache = {'uri': str(row.seturi), 'id': str(row.setid), 'label': str(row.setlabel) if row.setlabel else "", 'open': bool(row.setopen), 'empty': bool(row.setempty) }
              return self.mainsetcache
          raise DeepValidationError("Unable to find main set (set_uri=" + str(set_uri)+"), this should not happen")
docs: Returns information regarding the set