Re: foreign key constraint versus referential integrity constraint

On Oct 26, 10:29 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> Marshall wrote:
>
> >>>In a typed system, the type is whatever the intersection
> >>>of int and string is.
>
> >>Union not intersection. It has to be a type compatible with both integer
> >>and string.
>
> > I don't see how that would work. An integer isn't type compatible
> > with a string. Is it?
>
> It doesn't have to be compatible with a string. It only has to be
> compatible with TOP or the universal supertype. String doesn't have to
> be compatible with integer either. It only has to be compatible with TOP
> or the universal supertype.

OK, I didn't get much sleep last night so I'm not very sharp, but I'll just regurgitate the argument I thought of before I went to bed:

Consider relations A and B each with a single, common attribute. Natural join and inner union will behave much like intersection and union in this case. If the result type of the join isn't an intersection type, then we lose the property:

    A = A join (A union B)

because the type of the attribute of the expression is different than the type of the attribute of A.

More generally, the values in the result of a join are the intersection
of the values in the operands; why wouldn't the result type be the intersection type?

Also, what about the analogous situation with inner union? Would the type of the common attributes be a union type or an intersection type? The values are the union of the values of the operands, so I would propose that it has to be a union type.

> > Fortunately, I'm not hot any more. Now I'm thinking that
> > I haven't had any alcohol in a week or more. Maybe
> > a drink is in order? Plus, I think there is a cupcake in
> > a cupboard somewhere downstairs. I must away!
>
> Having bathed each of my 3 dogs several times, I now have to wash the
> skunk smell out of the vestibule before it pollutes the house any more
> than it already has, when I would much rather just go to bed.

Ouch! That sucks about the skunk.

I skipped the drink but I found the cupcake. It was getting a bit on the dry side but still quite tasty! Now it's time for me to make my son some pancakes and send him off to school.

Marshall Received on Tue Oct 27 2009 - 15:22:44 CET