def get_root_objective_ids(self):
url_path = construct_url('<STR_LIT>',<EOL>bank_id=self._catalog_idstr)<EOL>id_list = list()<EOL>for identifier in self._get_request(url_path)['<STR_LIT>']:<EOL><INDENT>id_list.append(Id(idstr=identifier))<EOL><DEDENT>return id_objects.IdList(id_list)<EOL>
Gets the root objective Ids in this hierarchy.

        return: (osid.id.IdList) - the root objective Ids
        raise:  OperationFailed - unable to complete request
        raise:  PermissionDenied - authorization failure
        compliance: mandatory - This method must be implemented.