Hi Don,

Havent looked at Michaels attachements in detail but seems to cover
the most obvious tree structures.

You also mention sets (unordered nasties; difficult to intrinsicaaly
identify). This is a particular problem to ORM/FCO-IM for which I
would advise you to have a look at the following:

http://www.fcoim.nl/Literature_Article_FCO.html

(this article also discusses recursive identification: trees; but
especially the discussion of the game of quamsplash is very
interesting)===> these do NOT map to relational model! There you
have make use of various techniques the most important of which is
called baptizing (inventing new identification strategies).

Ton