public function NotificationGetNotificationVersions($notification_items = NULL, $start, $end = NULL, $module_id = NULL)
 {
     // $notification_items : CbgrnNotificationItemVersionType class or this array
     // $start              : UNIX timestamp
     // $end                : UNIX timestamp (optional)
     // $module_id          : string (enum : grn.schedule, grn.message ....)
     $this->CheckAndSetHeader(__FUNCTION__);
     if ($notification_items !== NULL) {
         $reg_args["notification_item"] = $this->getRegularArgs($notification_items, __FUNCTION__, "CbgrnNotificationItemVersionType");
     }
     $reg_args["start"] = gmdate(W3C_DATETIME_FORMAT, $start);
     if ($end !== NULL) {
         $reg_args["end"] = gmdate(W3C_DATETIME_FORMAT, $end);
     }
     if ($module_id !== NULL) {
         $reg_args["module_id"] = $module_id;
     }
     $this->encodeString($reg_args);
     $results = parent::NotificationGetNotificationVersions($reg_args);
     $this->methodClose();
     return $this->decodeString($results->notification_item);
 }