Re: Relational Lattice, what is it good for?

Mikito Harakiri wrote:
> vc wrote:
> > Mikito Harakiri wrote:
> > [...]
> >
> > > A(x,y) || B(y,z) = { y | exists x A(x,y) or exists z B(y,z) }
> >
> > The above would be an empty set if both relations were empty, or an
> > undefined expression if either or both were non-empty since it's
> > unclear what domain 'y' ranges over.
>
> Let see:
>
> A(x, y) = {(1,a)}
> B(y, z) = {}
>
> Assuming domain y in {a} we have the inner union being {(a)}. Assuming
> domain y in {a,b} we still have the inner union being {(a)}.
>
> Where is domain dependence here?

I withdraw my objection. The 'y' domain is irrelevant. Received on Mon Feb 20 2006 - 02:31:56 CET