Re: Relational Lattice, what is it good for?

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? Received on Sun Feb 19 2006 - 12:17:42 CST