@abc.abstractmethod<EOL><INDENT>def get_functions_by_vaults(self, vault_ids):<DEDENT>
return<EOL>
Gets the list of ``Functions`` corresponding to a list of ``Vaults``.

        :param vault_ids: list of vault ``Ids``
        :type vault_ids: ``osid.id.IdList``
        :return: list of functions
        :rtype: ``osid.authorization.FunctionList``
        :raise: ``NullArgument`` -- ``vault_ids`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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