# Re: Sixth normal form

Date: Thu, 09 Aug 2007 11:53:16 -0700

Message-ID: <1186685596.209818.3680_at_d30g2000prg.googlegroups.com>

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:

*>
**>
**>
**>
**>
**> > 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.

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