Re: How to find Brothers and Sisters?

JOG a écrit :

> Cimode wrote:
>
> > David Cressey a écrit :
> >
> > > "Cimode" <cimode_at_hotmail.com> wrote in message
> > > news:1165242357.899497.161570_at_j44g2000cwa.googlegroups.com...
> > >
> > > >> I would think this is more a design flaw than the table not formally
> > > >> being in 1NF. No repeating groups. check. Data in the form of a
> > > >> relation. check. Some root entry in 'persons' who has himself or one of
> > > >> his successors as a father... erm.....hold on...
> > > >>
> > > >> (I think that Marshall once pointed out that the technical term for
> > > >> this is Furturama-NF, where Fry is his own grandfather)
> > > > Repeating groups is not the only prerequisite to state a table is in or
> > > > is not in 1NF.
> > >
> > > > There is no way you can be in 1NF if NULL values are permitted OR if
> > > > you have 2 different predicates in the same RTable...Only one predicate
> > > > per RTable.. That's by definition. Period.
> > >
> > >
> > > Where did you get that definition?
> > Check...
> > 06/03 #2: WHAT FIRST NORMAL FORM MEANS NOT by F. Pascal (Updated 03/04)
> > 06/03 #1: WHAT FIRST NORMAL FORM REALLY MEANS by C. J. Date
>
> couple of things. First, It annoys me these papers are not publically
> available. I understand one needs to earn a crust, but these seem
> fundamental issues and as such, it would be nice to see them out in the
> open.
>
> Second, as far as I am concerned 1NF requires data that fits into a
> relation. Hence no nulls or repeating groups. However, given Codd
> invented 1NF and was (in)famously a proponent of nulls, I am uncertain
> that the currently accepted definition of 1NF yet precludes them. This
> is sad of course, but we are still subject to these definitions, even
> though we promote their change.
>
> Third, there may be some confusion between schema and semantics. While
> the supplied table allows a nullable column, and hence should not be
> 1NF (although by many definitions including Codd's it is), this is
> wholly different from the knowledge we have that everyone must have a
> father. The latter is the design flaw I am referring to and it is
> important not to confuse the two in your answers to the OP.
It would not be ridiculous to assume that Codd himself underestimated the implications of his early discovery would put generations of people into forrmulate new mathematics to grasp such implications. Nevertheless, his work has been continued and several of his assumptions are either meant to be validated or invalidated by knowledgeable technical community. I do believe his later "tolerance" to NULL values, as opposed to the fundamental formulation that NULLS would break the link between mathematical set theory and computing, was meant for a purpose that will remain obscure.

After few years thinking about it, I formulated the following hypothesis:

> The later acceptance of NULLS was meant not to pull RM furthermore from its mathematical background to make it a independent area of research that could perdure on its own.
> The acceptance of NULLS was meant to trigger further research on RM limits and scope.
> Some other reason for which Codd's presence will be missed.

Given the probable assumption we are only at the early stage of discovering RM, I find safer to stick to fundamental refusal of NULLS until proven otherwise. After all, Codd has proven that NULL would break binary logic but the opposite still remain unproven. Received on Mon Dec 04 2006 - 23:19:27 CET