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>


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

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