Re: How to find Brothers and Sisters?

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. Received on Mon Dec 04 2006 - 19:18:29 CET