# Re: Proposal: 6NF

Date: 19 Oct 2006 05:33:41 -0700

Message-ID: <1161261221.437548.150820_at_m7g2000cwm.googlegroups.com>

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.

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> -- Jan Hidders

Received on Thu Oct 19 2006 - 14:33:41 CEST