<?php
define('DBHost', '127.0.0.1');
define('DBName', 'Database');
define('DBUser', 'root');
define('DBPassword', '');
require(dirname(__FILE__)."/src/PDO.class.php");
$DB = new Db(DBHost, DBName, DBUser, DBPassword);
?>
Why can't use ini file that puts credentials to main db function and link with main db php class, which won't require parameters to be required everytime. Just execute db() and go.