@abc.abstractmethod<EOL><INDENT>def get_ids_by_ids(self, ids):<DEDENT>
return<EOL>
Gets a list of ``Ids``.

        This method serves to get the principal ``Ids`` if different
        from the given ``Ids``.

        :param ids: a list of ``Ids``
        :type ids: ``osid.id.IdList``
        :return: a list of ``Ids``
        :rtype: ``osid.id.IdList``
        :raise: ``NotFound`` -- an ``id`` is not found
        :raise: ``NullArgument`` -- ``ids`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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