Problema con herencia

[anlhp]

asi es como lo puse en primera instancia y tampoco me funciona :s

public function __construct($_server = 'localhost', $_serverUser = 'root', $_serverPwd = null, $_serverDB = 'catalog2009'){
parent::__construct($_server, $_serverUser, $_serverPwd, $_serverDB) or die('<h2>There was an error connecting to the database.</h2>');
$this->success = true;
}