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

I too have been forced to filter some of the content of this newsgroup because of some posters' spam, so I can sympathize with his standpoint. I also believe being able to defend your ideas in the face of rigorous (and agressive) cross examination is one of the most valuable things about this group. It forces one to refine one's ideas and allows no room /whatsoever/ for sloppy thinking, and for me that has been an absolutely invaluable aid in improving my knowledge as quickly as possible.

When I first arrived here some of my opinions were naive to say the least and receiving short shrift was a bit of a shock, but with a thick skin and a willingness to accept there are more experienced people here, /hopefully/ my posts are now of more value.

Imo if occasionally one is misunderstood and it takes a post to provide clarification, or to indicate there was actually agreement, then that is only a small hassle compared to the benefits the discussion can offer as a whole.

David wrote:
> JOG wrote:
> > Bob Badour wrote:
> > > JOG wrote:
> > > > 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:
> > >
> > > You emphasized it and then David ignored it in his reply. If you look
> > > carefully, I think you will agree what you wrote appears "nowhere above"
> > > where I wrote "nowhere above".
> > >
> > >
> > > > 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!
> > >
> > > You missed the point that David constructed a straw man by ignoring your
> > > point entirely.
> >
> > Gotcha. All is clear. Happy new year.

>

>

>

>


>     person(P) :- P is a person


>     mother(M,C) :- M is the mother of child C

>     father(F,C) :- F is the father of child C

>

>