@abc.abstractmethod<EOL><INDENT>def get_assets_by_repositories(self, repository_ids):<DEDENT>
return<EOL>
Gets the list of ``Assets`` corresponding to a list of ``Repository`` objects.

        :param repository_ids: list of repository ``Ids``
        :type repository_ids: ``osid.id.IdList``
        :return: list of assets
        :rtype: ``osid.repository.AssetList``
        :raise: ``NullArgument`` -- ``repository_ids`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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