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Re: Normalisation

From: Jon Heggland <heggland_at_idi.ntnu.no>
Date: Tue, 5 Jul 2005 22:58:34 +0200
Message-ID: <MPG.1d3512e03d3a41939896e1@news.ntnu.no>


In article <PwBye.138032$Nn7.7012386_at_phobos.telenet-ops.be>, jan.hidders_at_REMOVETHIS.pandora.be says...
> > How does a set domain (e.g. the domain of sets of integers) violate
> > this? For definiteness, let's associate the normal set operations with
> > it---union, intersection, subset, cardinality and so on.
>
> By itself it doesn't. Until you start introducing operations that treat
> it as non-atomic. Then it does.

Does the common substring operation treat a string as non-atomic?

> > How does that help with normalisation?
>
> Since it defines atomicity it tells you when you are in 1NF or not. Just
> to be clear on this, I regard this discussion separate from the question
> whether you actually *should* be in 1NF or not.

That is nice to know. I assumed (as is generally done, I think) that relations in 1NF are in some sense better than relations not in 1NF (if such a thing is possible). If that is not the case, I find this discussion rather pointless.

> > And how can you say a priori that
> > a relvar with a set-valued attribute is not in 1NF, if that depends on
> > the operators of a particular DBMS?
>
> You cannot.

Yet you did say "Another option is to treat the field as a set-valued field (since it apparently can contain 0 or 1 values) which means that you are not in 1NF and should first normalize such that you are."

-- 
Jon
Received on Tue Jul 05 2005 - 15:58:34 CDT

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