@abc.abstractmethod<EOL><INDENT>def get_ids_by_authority_and_namespace(self, authority, namespace):<DEDENT>
return<EOL>
Gets ``Ids`` by the given authority and namespace.

        :param authority: an authority
        :type authority: ``string``
        :param namespace: a namespace
        :type namespace: ``string``
        :return: a list of ``Ids``
        :rtype: ``osid.id.IdList``
        :raise: ``NullArgument`` -- ``authority`` or ``namespace`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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