Re: foreign key constraint versus referential integrity constraint

On Oct 25, 11:06 pm, "Mr. Scott" <do_not_re..._at_noone.com> wrote:
> I think we should make the distinction, and formally.
>
> (p /\ q) -> r   is not the same as   (p -> r) /\ (q -> r)
> but  (p \/ q) -> r   is the same as   (p -> r) \/ (q -> r)

I don't follow. If these are BA expressions with the "->" as material implication, then

(p v q) -> r = ~(p v q) v r = (~p ^ ~q) v r (p -> r) v (q -> r) = (~p v r) v (~q v r) = (~p v ~q) v r

If the "->" is interpreted as deduction symbol (that is partial boolean lattice order), then

 (p v q) < r is not the same as (p < r) or (q < r) Received on Mon Oct 26 2009 - 17:27:58 CET