>for the purpose of discussion, pick one and explain why.

Fine, make things simple. ;-]

>Natural primary keys are a real problem in the unified semantic model --
>a single primary index that implements primary keys for all tables
>in a type hierarchy is flat impossible. About the only way out that
>I can think of is an artificial unique field in the root table. Any
>other ideas?

*ponderponder* It would be the responsability of the developer to define a
primary key that is valid for all tables in the hierarchy. That key must
then be unique across the tables. For example if I had a master table
Customers, 3 descendant tables Customers1, Customers2, Customers3, and
Customers defined a primary key of CUSTID, then a record in Customers1 could
not have the same CUSTID as a record in Customers3.

--
Mark Shapiro
Software Engineer
Segue Technologies, Inc.
http://www.seguetech.com/