# Re: Relational Lattice, what is it good for?

From: Mikito Harakiri <mikharakiri_nospaum_at_yahoo.com>

Date: 19 Feb 2006 10:17:42 -0800

Message-ID: <1140373062.081309.159880_at_g47g2000cwa.googlegroups.com>

Date: 19 Feb 2006 10:17:42 -0800

Message-ID: <1140373062.081309.159880_at_g47g2000cwa.googlegroups.com>

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 - 19:17:42 CET