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

From: x <x-false_at_yahoo.com>
Date: Mon, 7 Jun 2004 09:51:13 +0300
Message-ID: <40c40f73@post.usenet.com>

"Paul" <paul_at_test.com> wrote in message
news:SW1wc.11250$NK4.1467331_at_stones.force9.net...
> x wrote:
> >>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".
>
> In a DBMS, the constraint *would* stop you saying John is 84, that's the
> whole point of it. I presume that in Prolog it works in a similar way (I
> know, dangerous to talk about things I don't really know!). Surely Prolog
> wouldn't let you store two mutually contradictory statements?

Prolog will let you store anything you want that is expressible in Prolog. If you want contradictory statements, you can have them.

> > I'm not sure about this.
> > There must be exactly *ONE* real-world "interpretation" of the database.
>
> Why must there?
> consider the database with one tuple like this: (1,2)
> There could be many real-world interpretations of this database surely?
> It's not inconceivable that two people who've never met have identical
> databases with totally different interpretations.

Because otherwise the database would be ambiguous. :-) Define identical :-)

> >> > 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".
>
> OK maybe I shouldn't have used the world "just". But why can't a
> database be both? From a proof-theoretic point of view it's what I said.
> From a model-theoretic point of view it's what you said. The two aren't
> mutally exclusive.

But there is an exact match ? :-)

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Received on Mon Jun 07 2004 - 01:51:13 CDT

Original text of this message

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