public function byDeliveryExecution()
    {
        try
        {
            $this->checkMethod();

            $this->validateParams(array(self::DELIVERY_EXECUTION));

            $deliveryExecution = $this->getQtiResultService()->getDeliveryExecutionById(
                $this->getRequestParameter(self::DELIVERY_EXECUTION)
            );

            $this->returnValidXml($this->getQtiResultService()->getDeliveryExecutionXml($deliveryExecution));
        } catch (Exception $e) {
            $this->returnFailure($e);
        }
    }