Re: Functional Dependency to constrain a relation to exactly one element?

vc wrote:
> Marshall wrote:
> >
> > Well, we could always pair an empty determinant set FD with
> > an empty existential constraint. Or, given a candidate key k
> > of relation R, we could perhaps say
> >
> > exists R.k: forall R.k': k = k'
> >
> > (using x' to indicate a different binding of attribute x)
> >
> > Of course, you could make a good case that the above
> > isn't "simple".
>
> One would make a good case that it is not "existential" (why not
> "universal" ?) ;)

Well, that's a fair question. What do you call a constraint of the form "exists x: forall y: P(x,y)". What about the other order: "exists y: forall x: P(x,y)"? I'm inclined to call them by the type of the outermost quantifier, but I've never seen this addressed in a book.

Maybe the terminology isn't that important.

Hey, maybe we could string the quantifiers together, so we could have a uni-uni-exi-quantified statement. Or exi-uni-quantified.

Marshall Received on Mon Oct 02 2006 - 00:37:40 CEST