Re: In an RDBMS, what does "Data" mean?

From: x <x-false_at_yahoo.com>
Date: Thu, 3 Jun 2004 09:51:49 +0300
Message-ID: <40bec99c_at_post.usenet.com>

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"Paul" <paul_at_test.com> wrote in message news:dPtvc.10295$NK4.1397717_at_stones.force9.net...
> x wrote:
> > There are other differences. For example there are no candidate or
> > foreign keys in Prolog.
>
> Well candidate and foreign keys are really just special cases of
> constraints which have been given an elevated status. Can't you say in
> Prolog something like: "values in this column are unique" or "values in
> this column must also be in this other column in this other table"? (I'm
> not even sure if Prolog has tables or columns but I guess it must have
> something analogous)

Relational databases and Prolog "databases" are different beasts. There are no integrity constraints in Prolog.

> > But I'm interested in properties of a particular structure S, not in
> > the properties of some theory T that happen to describe some aspects
> > of S.

> But first-order logic is "special" in some sense because it is the very
> foundation of everything you do. It's the theory T above, we're not
> interested in any specific structure S, we just want to know that for
> any S, first-order logic does enable us to talk about S completely (in
> the sense defined above). This is the very definition of what it means
> for first-order logic to be complete. What the properties of any
> particular structure S are is a totally different question.

Yes. I know first-order logic is "special". But there is a difference in interests.
One may be interested in a particular field of work and will use any theories that might help.
One may be interested in a particular theory and its applications.

> >> I'm acutally wondering as well whether all this talk of Godel is
> >> irrelevant anyway because in databases we are only dealing with
> >> finite sets of axioms. Possibly second order logic is complete when
> >> you have a finite number of axioms? I'll have to do a bit more
> >> Googling.
> >
> > In databases we deal with facts, not with finite sets of axioms.
>
> I'm saying these are the same thing. Each tuple is a logical
> proposition, a fact, which is an axiom in our database (our "theory").

I'm not sure about this.
I'm not sure a database is a theory.
I'm not sure a database is a finite set of axioms.

And the set of facts in a database can grow arbitrary large (theoretically speaking).

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Received on Thu Jun 03 2004 - 08:51:49 CEST