@abc.abstractmethod<EOL><INDENT>def delete_relationship(self, relationship_id):<DEDENT>
pass<EOL>
Deletes a ``Relationship``.

        :param relationship_id: the ``Id`` of the ``Relationship`` to remove
        :type relationship_id: ``osid.id.Id``
        :raise: ``NotFound`` -- ``relationship_id`` 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.*