Re: More on lists and sets

Brian Selzer wrote:
> "Jan Hidders" <hidders_at_gmail.com> wrote in message
> news:1143452308.856695.294440_at_z34g2000cwc.googlegroups.com...
> > Brian Selzer wrote:
> >>
> >> The problem with NFNF models is the introduction of redundancy and second
> >> order predicate logic.
> >
> > NFNF models do not necessarily introduce redundancy. And neither is the
> > logic that is required to deal with them a problem. Note that just as
> > we only use a restricted subset of first-order logic for the flat
> > relational model, you would also only use a restricted subset of
> > second-order logic fo the nested relational model, and the prevents any
> > theoretical problems.
>
> They certainly can. I don't have time right now to provide an example, but
> maybe I'll get to it this evening.

Please do, and make sure you use a typed higher order logic.

> >> Issues that are solved through the application of
> >> higher normal forms reappear with the introduction of composite
> >> attributes.
> >
> > Such as? In fact, the reverse true. It is for example known that in
> > some cases normalization to BCNF while being dependency preserving is
> > not possible in the flat model, but is in fact possible in the nested
> > relational model (given appropriate generalizations of dependencies and
> > normal forms).
>
> If a tuple with a list is deleted, the contents of the list is also deleted,
> possibly snuffing out the only instance of that list in the database. This
> may not be a problem in most cases, but wasn't this same scenario one of the
> arguments for further normalization?

No. It's the same scenario as where you delete a tuple with the last occurrence of the date of March 27th 2006. If that is problematic you have made a data modelling error.

> The problem caused by the lack of dependency preservation can be overcome in
> several ways, such as by using surrogates or circular inclusion
> dependencies.

No. It cannot.

• Jan Hidders