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

• Post for FREE via your newsreader at post.usenet.com ****

"Paul" <paul_at_test.com> wrote in message news:ckHvc.10429$wI4.1251077_at_wards.force9.net...
> x wrote:
> > Relational databases and Prolog "databases" are different beasts.
> > There are no integrity constraints in Prolog.
>
> Integrity constraints are really just expressions of first-order
> predicate logic. Prolog stores expressions of predicate logic, so surely
> it can do them? I think the difference might be that Prolog doesn't
> distinguish between "data" and "constraints" in the way that relational
> databases do.
>
> consider the statements:
> 1) Pete is 29 years old.
> 2) Everyone's age is under 60.
>
> In a relational database the first would be data and the second a
> constraint. In Prolog would they both be data?

Nothing would stop you to say John is 84 years old. It just follows that John isn't "everyone".

> > 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.
>
> Here's another refereence:
> http://en.wikipedia.org/wiki/G%F6del's_completeness_theorem
> "in first-order predicate calculus every universally valid formula can
> be proved... A logical formula is called universally valid if it is true
> in every possible domain and with every possible interpretation, inside
> that domain, of non-constant symbols used in the formula."

There is no need to provide more references. I am aware of that.
The key word here is "complete".
What is "complete" for one, it isn't "complete" for everyone.

<quote>
The rules are "complete" in the sense that they are strong enough to prove every universally valid statement. It was already known earlier that only universally valid statements can be proven in first-order logic. </quote>

> >>> 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 guess anything can be regarded as a theory in the right context.
> In terms of Godel's Completeness Theorem you have:
>
> 1) first-order logic itself (corresponding to the DBMS)
> 2) various theories we talk about using logic (corresponding to databases)
> 3) various models of the theories (the real-world interpretations of the
> databases)
>
> 1) is the meta-language, 2) is the syntax and 3) is the semantics.
> Godel's Completeness Theorem says: suppose you talk about a theory with
> first-order logic. Then if something is true in every possible semantics
> for that model, it is provable using syntax alone.

I'm not sure about this.
There must be exactly *ONE* real-world "interpretation" of the database.

> > I'm not sure a database is a finite set of axioms.
>
> Why not? A databases is just a finite set of tuples from which you
> derive other truths.

It is not. It is a one-to-one corespondence with a piece of the "real-world".

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

• Usenet.com - The #1 Usenet Newsgroup Service on The Planet! *** http://www.usenet.com Unlimited Download - 19 Seperate Servers - 90,000 groups - Uncensored -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=