@abc.abstractmethod<EOL><INDENT>def register_for_changed_relationship(self, relationship_id):<DEDENT>
pass<EOL>
Registers for notification of an updated relationship.

        ``RelationshipReceiver.changedRelationships()`` is invoked when
        the specified relationship in this family is changed.

        :param relationship_id: the ``Id`` of the ``Relationship`` to monitor
        :type relationship_id: ``osid.id.Id``
        :raise: ``NullArgument`` -- ``relationship_id`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

        *compliance: mandatory -- This method must be implemented.*