protected function checkItemChildType($parentType,$childType)
	{
		static $types=array('operation','task','role');
		if($parentType < $childType)
			throw new CException(Yii::t('yii','Cannot add an item of type "{child}" to an item of type "{parent}".',
				array('{child}'=>$types[$childType], '{parent}'=>$types[$parentType])));
	}