>>Actually, then I heard from someone, in a discussion on the subject, that the most complicated and largest contraption in use, an ocean liner, didn't go deeper than ten levels.
>
>Last statement is interesting. Of course, once you go beyond one level the only approach that makes sense is a self-referencing/recursive one.
>

Which fits the general rule that in the database business, there are only three quantities: 0, 1 and many.

Tamar