Re: Sixth normal form

Although your comments in this thread are knowledgeable and useful I 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:
>
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> > On Aug 1, 7:36 am, Jan Hidders <hidd..._at_gmail.com> wrote:
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> > > 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.
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.

> > The other thing here which is maybe with a questionable meaning is
> > "The only somewhat mysterious part...". This seems like there are
> > some other parts in definition of 5NF.
>
> You may want to check your irony-meter. It seems broken. :-)
>
> > Now we can set the question - why mentioned procedure for misterios
> > part is combination of formal and intuitive. Although, mentioned
> > procedure is useful, I beleive it is good to be aware of the
> > following:
>
> > a) Cks are based on FDs and for FDs there is a formal system.
> > b) For JDs there is no formal system in the sense of complete
> > inference rules.
>
> JDs have been succesfully axiomatized. In fact, much larger classes
> including MVDs, FDs and much more have been axiomatized. See the Alice
> book for a wealth of information on that.
>
> -- Jan Hidders- Hide quoted text -
>
> - Show quoted text -

Vladimir Odrljin Received on Thu Aug 09 2007 - 20:53:16 CEST