Código PHP:
$thisFile = str_replace('\\', '/', __FILE__);
$docRoot = $_SERVER['DOCUMENT_ROOT'];
$webRoot = str_replace(array($docRoot, 'library/config.php'), '', $thisFile);
$srvRoot = str_replace('library/config.php', '', $thisFile);
define('WEB_ROOT', $webRoot);
define('SRV_ROOT', $srvRoot);
gracias