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Re: Normalisation

From: Jon Heggland <heggland_at_idi.ntnu.no>
Date: Fri, 8 Jul 2005 11:15:29 +0200
Message-ID: <MPG.1d385e09db0b29629896ed@news.ntnu.no>


In article <Ezeze.139544$p21.7384199_at_phobos.telenet-ops.be>, jan.hidders_at_REMOVETHIS.pandora.be says...
> >>Ah, but now you are using the domain or relations, right? There is a
> >>problem with that domain. It doesn't exist. The collection of all
> >>relations is a proper class, and not a set, but domains have to be sets.
> >
> > You'll have to educate me on the difference between "proper class" and
> > "domain", I'm afraid. The term "class" is used for so many slightly
> > different things.
>
> http://en.wikipedia.org/wiki/Class_(set_theory)

Call me stupid, but you still have to explain to me why the "collection" of relations is not a set. I can't figure out from Wikipedia what it is that disqualifies something from being a set.

Are you saying that the "domain of sets" is not a domain either?

And that relation-valued and set-valued attributes are contradictions in terms, since relation and set are not domains?

> > Should I be forbidden from treating "relation" as a (generic) domain
> > when defining this operator? Why?
>
> Because by definition it isn't, and redefining the notion of domain such
> that it is, is not that easy without either running into paradoxes or
> getting a notion which it is almost impossible to reason about.

Can you give me any examples of trouble arising from this? And an explanation why the relational operators do not run into paradoxes? Or do they?

> > Would you allow this operator if it were system-defined?
>
> I am not disallowing anything.

Please don't be coy or cryptic. Do you mean that *you* do not disallow anything, but mathematical theory does? Or that being forbidden and being disallowed is different?

-- 
Jon
Received on Fri Jul 08 2005 - 04:15:29 CDT

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