Re: Nulls, integrity, the closed world assumption and events

Bob Badour wrote:
> Marshall wrote:
>
> > On Jan 8, 4:44 am, "David" <davi..._at_iinet.net.au> wrote:
> >
> >>My point is that the following six conditions can't all be satisfied at
> >>once
> >> C1. use person(P,M,F) relation
> >> C2. don't allow nulls in M,F
> >> C3. enforce referential integrity on M,F
> >> C4. only allow finite number of persons in the domain
> >> C5. there are no cycles in the family tree
> >> C6. there is at least one person
> >>
> >>Obviously we must have C4, C5 and allow C6. I suggest that C2,C3 are
> >>important and therefore C1 should be dropped. ie the person(P,M,F)
> >>relation itself is "bad". Do you agree?
> >
> > This analysis looks right to me.
>
> Huh? Your solution basically achieves all of the above with the
> inconsequential difference that you used a different name for the
> relation in C1.
>
> Nowhere above does it mention the very consequential difference in
> referential integrity constraints, which is in fact the straw in the man.

Hi Bob, if you were referring to my post then your last statement isn't true. I emphasized the change in referential integrity constraints as being important:

JOG wrote
> where P is the candidate key of _parentage_, but where P, M and F have
> enforced referential integrity (with a check constraint on sex) back to
> the _person_ relation

Either I've missed your point or you had a heavy new years celebration this year! Received on Tue Jan 09 2007 - 12:59:56 CET