Tree Structures and Overlap

I'm sure that this one will be bouncing around as a more popular meme, as this comes via Clay Shirky, but in terms of too neat organisational structures, this article by Christopher Alexander called A City is Not a Tree resonates with information architecture and the need for cross-linking and related items in a tree structure. I know that there is a great deal of debate about the navigation metaphor and the concept of cyberspace in terms of IA at present, but it is sometimes nice to take a hint from the real physical world. In this case, the real world shows itself to be hyperlinked in a way, not neatly bundled into patterns and single classifications...but we knew that anyway. I'm rambling, so I'll stop.