/**
  * Constructor
  * 
  * @param array $params Database column fields which should be returned
  * @access private 
  * @return void 
  */
 function materialized_path_driver()
 {
     parent::tree_db_driver();
 }
	/**
	* Constructor
	* 
	* @param array $params Database column fields which should be returned
	* @access private 
	* @return void 
	*/
	function nested_sets_driver()
	{		
		parent :: tree_db_driver();
	}