@abc.abstractmethod<EOL><INDENT>def get_relationship_form_for_update(self, relationship_id):<DEDENT>
return<EOL>
Gets the relationship form for updating an existing relationship.

        A new relationship form should be requested for each update
        transaction.

        :param relationship_id: the ``Id`` of the ``Relationship``
        :type relationship_id: ``osid.id.Id``
        :return: the relationship form
        :rtype: ``osid.relationship.RelationshipForm``
        :raise: ``NotFound`` -- ``relationship_id`` is not found
        :raise: ``NullArgument`` -- ``relationship_id`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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