def sequence_objectives(self, parent_objective_id=None, objective_ids=None):
raise Unimplemented()<EOL>
Sequences a set of objectives under a parent.

        arg:    parent_objective_id (osid.id.Id): the Id of the parent
                objective
        arg:    objective_ids (osid.id.Id[]): the Id of the objectives
        raise:  NotFound - parent_id or an objective_id not found, or an
                objective_id is not a child of parent_objective_id
        raise:  NullArgument - parent_objective_id or objective_ids is
                null
        raise:  OperationFailed - unable to complete request
        raise:  PermissionDenied - authorization failure
        compliance: mandatory - This method must be implemented.