def get_relationship_form_for_update(self, relationship_id=None):
if relationship_id is None:<EOL><INDENT>raise NullArgument()<EOL><DEDENT>try:<EOL><INDENT>url_path = ('<STR_LIT>' +<EOL>self._catalog_idstr + '<STR_LIT>' + str(relationship_id))<EOL>relationship = objects.Relationship(self._get_request(url_path))<EOL><DEDENT>except Exception:<EOL><INDENT>raise<EOL><DEDENT>relationship_form = objects.RelationshipForm(relationship._my_map)<EOL>self._forms[relationship_form.get_id().get_identifier()] = not UPDATED<EOL>return relationship_form<EOL>
Gets the relationship form for updating an existing relationship.

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

        arg:    relationship_id (osid.id.Id): the ``Id`` of the
                ``Relationship``
        return: (osid.relationship.RelationshipForm) - the relationship
                form
        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.*