docs: def is_parent(self, id_, parent_id):
          """Tests if an ``Id`` is a direct parent of another.
  
          arg:    id (osid.id.Id): the ``Id`` to query
          arg:    parent_id (osid.id.Id): the ``Id`` of a parent
          return: (boolean) - ``true`` if this ``parent_id`` is a parent
                  of ``id,``  ``false`` otherwise
          raise:  NotFound - ``id`` is not found
          raise:  NullArgument - ``id`` or ``parent_id`` is ``null``
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure
          *compliance: mandatory -- This method must be implemented.*
          *implementation notes*: If ``parent_id`` not found return
          ``false``.
  
          """
          return bool(self._rls.get_relationships_by_genus_type_for_peers(
              parent_id,
              id_,
              self._relationship_type).available())