# Re: Proposal: 6NF

Date: 19 Oct 2006 09:44:23 -0700

Message-ID: <1161276262.975206.249300_at_f16g2000cwb.googlegroups.com>

vc wrote:

*> Jan Hidders wrote:
**> > vc wrote:
**> > > 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, [....].
**> >
**> > You keep on making the same mistake. The expression a +[mod 4] b has a
**> > well defined result if a and b are from any subset of {0, 1, 2, 3}.
*

> >

> Consider the subset {2, 3}. What is the result of (2+3) mod 4 ? If

*> you say it's '1', what is '1'? There is no such element in {2, 3}.*

*> [snip]*

Mathematically, surely the modulo addition operation as described above above can be applied to the subset {2, 3}, while happily having a closure of {0,1,2} for instance? After all, any operation just maps one set of values to another - why the self-closure requirement?

I stand ready for correction if I have made a misinterpretation. Received on Thu Oct 19 2006 - 18:44:23 CEST