Re: Sixth normal form

On 7 aug, 22:34, vldm10 <vld..._at_yahoo.com> wrote:
> 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.
>
> > > 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 -
>
> There is no irony in my post. I am sorry, that you understood this as
> an irony.

Don't be sorry. I didn't. I was only pointing out that there was irony in *my* posting.

• Jan Hidders