Re: NULLs: theoretical problems?

"David Portas" <REMOVE_BEFORE_REPLYING_dportas_at_acm.org> wrote in message news:1186837357.596324.154260_at_q75g2000hsh.googlegroups.com...
> On 11 Aug, 12:20, Jan Hidders <hidd..._at_gmail.com> wrote:
> >
> > Heck, I could even explain it in Dutch for you. ;-)
> >
> > But also then it wouldn't make sense. Any argumentation that is based
> > on taking the definitions in standard normalization theory and
> > applying them to relations with null values is based on a fallacy. If
> > you really want a meaningful discussion you first need to come up with
> > a proper formal definition of a relation with null values, update
> > anomalies, redundancy, dependencies, et cetera. That, by the way, is
> > actually not as hard as you might expect, but it still needs to be
> > done.
> >
> > -- Jan Hidders
>
> Jan, I agree with you. I don't know of any such formal definition that
> deals with nulls. What I was trying (and probably failing) to do was
> to show that by the present definitions we cannot find nulls to be
> acceptable in dependencies or in normalized relations. I was trying to
> do so without commenting on whether nulls can be permitted in
> relations at all (but naturally I agree that they can't).

It seems to me, after looking at it for a couple of decades, that nulls cannot be permitted in relations at all, but that they can be permitted in tables that represent relations.

SQL tables are approximately tables that represent relations. The mapping isn't perfect, so some of the formal properties of relations do not carry over to SQL tables. This has been the source of much debate and friction in this newsgroup and in other forums. Much of that debate and friction is unnecessary. Much ado about nothing.

The renaming of nulls to be a "special value" is, as far as I'm concerned, a deft side-step rather than a fundamental resolution. To me, the fundamental problem that nulls address is about the relationship between representations and the reality they purport to represent. This relationship between representation and reality is complex and subtle, and pervades almost all of computer science, not just database theory. Received on Sat Aug 11 2007 - 15:39:05 CEST