I was just browsing around and found this article. Great theories but why would you ever want to store hierarchical data in a flat database? Unless of course it was the only choice you had it seems like a bad idea to me. The first way takes too much system resources and the second has to have the tree rebuilt everytime you add a row to the table. Icky. I'd say this is the perfect situation for an XML database. An article that explores the XML database options for heirarchical data and php would be a great companion for this article. Anyone know of a good one?