private function getShownStructure()
    {
        if($this->hasRequestParameter('shownStructure')){
            $structure = $this->getRequestParameter('shownStructure');
            $perspectives = \oat\tao\model\menu\MenuService::getAllPerspectives();
            foreach($perspectives as $perspective){
                if($perspective->getId() == $structure){
                    return $perspective->getId();
                }
            }
        }
        return null;
    }