>Dragan
>
>I agree completely. There was a case where we had a tree structure implemented that would not practically go more than 8 levels deep. It was in Sybase and we didn't have quite the SQL set of commands that were available in SQLServer. To get the absolute best performance out we hard coded a SP to do 10 self joins, with the code that did the tree maintenence to burp out an error message should they ever attempt to make the tree more than 10 levels deep. It was something like 50 times faster to hardwire the self-joins than it was to do any sort of iterative loop through the tree.

The most complicated human structure that I know this about - an ocean liner - has ten levels of assembly (i.e. parts which are assembled from parts which are assembled etc). I guess a space shuttle or a Mars vehicle may have an equally deep tree structure, maybe 12 levels, but I doubt that - each level has to have something that's physically containing smaller parts. Just folding paper ten times gives you a piece that's 1024 times thicker than the original. Even an absolute address of a person may not go beyond that - country, region, city, street address, person's name - that's five levels, and the region can be actually skipped. Going deeper, you may want to address each individual cell of his body, you may need few levels more (organ, tissue, cell ID). And that's it - unless you want to address an individual atom in the known universe.