Marshall wrote:
> On May 6, 11:21 pm, Jon Heggland <jon.heggl..._at_idi.ntnu.no> wrote:
>> Are you familiar with TTM's IM prescription 13: Join etc. with
>> inheritance? Are you able to reconcile your preference with that?
>
> Is that the one that says the type of an attribute in the result
> of a join is the most common specific supertype? If so,
> yes I am familiar, and no, I can't reconcile it. I don't see
> any reason to prefer a type that's more general than necessary.
The crux of the matter in that prescription is the equivalence between
R1 & R2 and R1 - (R1 - R2). How do you handle that?
--
Jon
Received on Mon May 07 2007 - 06:15:57 CDT
