protected function getTargetNode(ObjectId $targetOID) {
    if ($this->targetNode == null) {
      // load parent node
      $persistenceFacade = $this->getPersistenceFacade();
      $targetNode = $persistenceFacade->load($targetOID);
      $this->targetNode = $targetNode;
    }
    return $this->targetNode;
  }