def get_relationship_query_session(self):
        """Gets the ``OsidSession`` associated with the relationship query service.

        return: (osid.relationship.RelationshipQuerySession) - a
                ``RelationshipQuerySession``
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - ``supports_relationship_query()`` is
                ``false``
        *compliance: optional -- This method must be implemented if
        ``supports_relationship_query()`` is ``true``.*

        """
        if not self.supports_relationship_query():
            raise errors.Unimplemented()
        # pylint: disable=no-member
        return sessions.RelationshipQuerySession(runtime=self._runtime)