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

Cimode wrote:
> David wrote:
> > Consider the following relation
> >
> > person(P,M,F) :- person P has mother M, father F.
> >
> > By induction a non-empty
> > database would have to be infinite.
>
> A false premise makes all deductions coming from it false.

No. If we show p => q and p is false then we can't deduce q is false.

> Closed
> World Assumption does not say anything about the number of element that
> belong to a domain of values from which one attribute values are
> derived. In the case of a *person* domain, the number of elements in
> the set is certainly finite. Therefore, the number of propositions
> involving person as an attribute is limited as well.

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?

David Received on Mon Jan 08 2007 - 13:44:07 CET