@abc.abstractmethod<EOL><INDENT>def alias_relationship(self, relationship_id, alias_id):<DEDENT>
pass<EOL>
Adds an ``Id`` to a ``Relationship`` for the purpose of creating compatibility.

        The primary ``Id`` of the ``Relationship`` is determined by the
        provider. The new ``Id`` performs as an alias to the primary
        ``Id``. If the alias is a pointer to another relationship, it is
        reassigned to the given relationship ``Id``.

        :param relationship_id: the ``Id`` of a ``Relationship``
        :type relationship_id: ``osid.id.Id``
        :param alias_id: the alias ``Id``
        :type alias_id: ``osid.id.Id``
        :raise: ``AlreadyExists`` -- ``alias_id`` is already assigned
        :raise: ``NotFound`` -- ``relationship`` not found
        :raise: ``NullArgument`` -- ``relationship_id`` or ``alias_id`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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