Preventing Multiple Inheritance

Hi-

Let's say I have a base table B (with a PK id, say) and two derived
tables D1 & D2 (with different cols).  For a given B.id, I'd like to
allow only a corresponding row in *either* D1 or D2, but not both.  Any
suggestions on how to do this? Should I not be using inheritance at all?

My thought was to add a column inherits_to to B with a value indicating
whether that row is really a D1 or a D2 and enforce it with appropriate
CHECK constraints on each of the derived tables.

Sorry if this is unclear...

--
Peter Fein                 pfein@pobox.com                 773-575-0694

Basically, if you're not a utopianist, you're a schmuck. -J. Feldman