require() and directory structures

[Anon]

It took me a while but I looked through just about every message on the forums and I wasn't able to find the answer to my question.
Here is my situation in a nutshell:
You have a x.php file that wants to require a file y.inc that is in a subdirectory, and that required file wants to include another file z.inc in that same subdirectory.
Why do I get an error if I don't make the require in y.inc require("subdir/z.inc"); even though z.inc is in the same directory as y.inc? That makes absolutely no sense to me. If I have another file that is in the parent directory of x.php that also needs to require y.inc the paths are wrong again.

This causes problems in different parts of my website. The website is getting quite large and the directory structure is complex. Can I use absolute paths instead of the somewhat relative paths?

[Anon]

It appears that the way require() works is it brings the file in as if the file was inline in the current script.

For a project I'm working on, I'm using a tip that I found in a tutorial where you create a configuration object and then attach default paths to that object...

<?
// env init script

class object {}

$CFG = new object();

$CFG->incdir = '/var/www/html/includes';

?>

and then in your scripts/functions, you would put something like this....

<?

global $CFG;

require("$CFG->incdir/x.inc");

?>