docs: def get_root_objective_bank_ids(self, alias):
          """Gets the root objective bank Ids in this hierarchy.
  
          return: (osid.id.IdList) - the root objective bank Ids
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure
          compliance: mandatory - This method must be implemented.
  
          """
          url_path = self._urls.roots(alias)
          return self._get_request(url_path)