# Re: Sixth normal form

From: Jan Hidders <hidders_at_gmail.com>
Date: Fri, 10 Aug 2007 11:08:26 -0000

On 9 aug, 20:53, vldm10 <vld..._at_yahoo.com> wrote:
> have a few remarks here.
>
> On Aug 7, 3:30 pm, Jan Hidders <hidd..._at_gmail.com> wrote:
>
>
>
> > On 7 aug, 20:36, vldm10 <vld..._at_yahoo.com> wrote:
>
> > > On Aug 1, 7:36 am, Jan Hidders <hidd..._at_gmail.com> wrote:
>
> > > > Any attempt to reformulate it to something easier or more intuitive in
> > > > my experience almost always ends up with something that is either
> > > > wrong or actually harder to understand.
>
> > > > The only somewhat mysterious part may be the "JD is implied by the
> > > > CKs" but this can be tested by the following simple procedure:
>
> > > > 1. Let jd be the join dependency we want to test
> > > > 2. While jd has two elements (being sets of attributes) Si and Sj such
> > > > that the intersection of Si and Sj contains a candidate key do:
> > > > 2.1 replace Si and Sj with the union of Si and Sj
> > > > 3. If jd contains the header of the relation (which is also a set of
> > > > attributes) then return "yes" else "false"
> > > > -- Jan Hidders
>
> > > You gave here the procedure which is more on intuitive level than
> > > based on some formal system.
>
> > Although somewhat informally described by me, it is a proper algorithm
> > and as such *is* a formal system that has been proven both sound and
> > complete.
>
> I have a feeling that you didn't pay enough attention to make a
> distinction between a constructioun (construct) and a formal axiomatic
> system (FAS). I mean here on construction for 5NF and 6NF, that put
> "things" in 5NF, 6NF.

Indeed, the algorithm is not a formal axiomatic system, but it is a formal system in the broader sense of the word. And if you look closely you will see that it is in fact based on a very simple axiomatic system whose propositions are JDs and CKs and has one inference rule that allows you to derive JDs. And that axiomatic system has been proven to be sound and complete.

> For example your explanation in this thread that 6NF : "Informaly put
> it says that every distinct fact gets its own relation...", I am
> afraid this does not have sense and probably is naive, regarding the
> constructs for 6NF.

You are entitled to your opinion, of course.

• Jan Hidders
Received on Fri Aug 10 2007 - 13:08:26 CEST

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