Tree structure / access rights and associations

Hello,

in an application I was working on recently, we had to develop a system
to grant access rights on and associate items with parts of a tree.
Imagine for example a tree of product categories in an e-shop - you
might want to associate items with these categories with categories
(once you associate the item to a category, it's associated to it's
parent category too) and grant access rights on subtrees to
administrators (once you grant access to a category, you're granting
access to it's subcategories too).

Inspired by the solution we developed, I've implemented a similar system
and I'm releasing it under GPL license. All the sources (basically a set
of triggers) along with documentation etc. can be found here:

http://www.fuzzy.cz/databaze/index-en.php

Tomas