protected function doRead()
 {
     parent::doRead();
     if ($this->ref_id) {
         include_once "./Services/Object/classes/class.ilObjectActivation.php";
         $activation = ilObjectActivation::getItem($this->ref_id);
         switch ($activation["timing_type"]) {
             case ilObjectActivation::TIMINGS_ACTIVATION:
                 $this->setActivationLimited(true);
                 $this->setActivationStartDate($activation["timing_start"]);
                 $this->setActivationEndDate($activation["timing_end"]);
                 $this->setActivationVisibility($activation["visible"]);
                 break;
             default:
                 $this->setActivationLimited(false);
                 break;
         }
     }
 }