SITE_ROOT = Variable?

I'd very much appreciate if someone could help me with a solution.

How can I get this:

d开发者_运维问答efine ('SITE_ROOT', $_SERVER['DOCUMENT_ROOT'] . SITE_BASE);

to look something like this:

define ('SITE_ROOT', [variable from root.com/directory/data.php] );

Many thanks.

---

<?php
    include_once("/directory/data.php");
    define('SITE_ROOT', $variable);
?>