public function getResponse(){
        $returnValue = null;

        $responseAttribute = $this->getAttribute('responseIdentifier');
        if(!is_null($responseAttribute)){
            $idenfierBaseType = $responseAttribute->getValue(true);
            if(!is_null($idenfierBaseType)){
                $returnValue = $idenfierBaseType->getReferencedObject();
            }else{
                $responseDeclaration = new ResponseDeclaration();
                if($this->setResponse($responseDeclaration)){
                    $returnValue = $responseDeclaration;
                }else{
                    throw new QtiModelException('cannot create the interaction response');
                }
            }
        }

        return $returnValue;
    }