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From: "vc" <boston103@hotmail.com>
Newsgroups: comp.databases.theory
Subject: Re: Proposal: 6NF
Date: 19 Oct 2006 05:33:41 -0700
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Jan Hidders wrote:
[...]

A much simpler example.  Let {0, 1, 2, 3} be a set of four integers
with addition modulo 4.  Then,  none of its subsets,  except {0} and
{0, 2},  retains the addition mod 4 operation which makes the idea of
'subtype as subset' utterly silly, as it would with respect to just
about any common math structure.

Also,  the OOP hypothetical programmer would expect that a subtype
would have, informally speaking,  *more*
properties/operations/'methods',  not less:  the basic class properties
plus some new ones.  So at the intuitive level with typical languages
like Java, 'subtype as subset'  does not make much sense either,  at
least with respect to even the simplest mathematical objects.

> 
> -- Jan Hidders