Re: Question on 5NF

From: <davide.mauri_at_gmail.com>
Date: 12 Oct 2006 14:34:49 -0700
Message-ID: <1160688889.117575.216720_at_i42g2000cwa.googlegroups.com>


> > I found myself in a situation where I have the following rule (speaking
> > using wikipedia sample's terms): the Condition that the Insurance
> > provider can cover are *only* those conditions covered by the
> > Psychiatrist which are affiliated with that Insurance Provider.
>
> That's actually not a static constraint, and that's what normalization
> deals with, so your question is not really a normalization question. To
> understand why it's not a static constraint try to formulate it as a
> logical constraint on the relation. You get something like:
>
> "for every tuple (P,I,C) in the relation there is a tuple (P',I',C') in
> the relation such that I=I' and C=C' "
>
> Which is a tautology. But if you formulate it as a dynamic constraint
>
> "you can add a tuple (P,I,C) in the relation if there is already a
> tuple (P',I',C') in the relation such that I=I' and C=C' "
>
> then it makes sense. :-)
>

Ok :-)

>
> Depends on what FDs, MVDs and JDs you think hold. In particular you
> haven't told us yet if the JD that might lead to a split of PIC
> actually holds or not. Presuming that it does and there are no further
> non-trivial FDs and MVDs then you are not in 5NF.

But if there aren't non-trivial FDs and MVDs shouldn't I be in 5NF?

>
> -- Jan Hidders

Thanks Jan!

Davide Received on Thu Oct 12 2006 - 23:34:49 CEST

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