Database-Driven Tree Structures with XML and XSLT
http://www.contentwithstyle.co.uk/Articles/32/database-driven-tree-structures-with-xml-and-xslt

Opitz, Pascal
Content with Style
2005

Abstract:

This article deals with the display of tree-structures that are driven by a database. There are actually a few approaches to transform a 2-dimensional structure into a tree, and it seems odd that most are unknown to many developers.