Re: In an RDBMS, what does "Data" mean?
Date: Fri, 28 May 2004 18:33:11 +0300
Message-ID: <40b75ad7$1_at_post.usenet.com>
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"Paul" <paul_at_test.com> wrote in message
news:40b74ea7$0$1049$ed2619ec_at_ptn-nntp-reader02.plus.net...
> Dawn M. Wolthuis wrote:
> >> I'm just talking about the system of logic that enables us to talk
> >> about our database (our "theory" if you like). Whether our theory
> >> has axioms that correspond to the real world, or whether our
> >> interpretation (or "model") of our theory is accurate, is a totally
> >> different question.
> >
> > Exactly -- so I think you and Wol (and I) are in agreement on that.
> > It is why whenever anyone suggests that the best way to set up a
> > databases is by employing relational theory BECAUSE relational theory
> > is based on mathematics, I laugh (then cry).
>
> Why? This seems like a reasonable statement. Suppose for example we
> based our DBMS on second-order logic. Then theory tells us we will have
> incompleteness (ignoring the fact that databases are finite!). So this
> would tell us that the mathematical part of the DBMS is on shaky ground.
> As it happens that DBMSs use first-order logic, we know it is rock-solid
> because of Godel's Completeness Theorem. That seems very reassuring to
> me. Maybe this point seems so obvious that people just take it for
> granted - they don't even realise that there is something to be proved
> in the first place.
>
> Now it may well be that the "multivalue" database model also just uses
> first-order logic presented in a slightly obfuscated way, in which case
> you'd have the peace of mind for that as well.
Prolog is based on first order logic.
What is the difference between the Prolog way and the Relational Model way
of representing data ?
> > 3) Are we applying the best, most effective, most efficient, etc
> > metaphor or is there something better to either supplement or replace
> > it?
>
> I think we are. I think the insight that Codd had was to start with
> logic and build upwards from there, instead of putting together an
> ad-hoc data model first and then trying to reconcile it downwards to
logic.
>
> I think the only ways we could go would be to different logics e.g.
> multi-valued logic or "fuzzy" logic etc. I don't claim to know what
> these all are but a search should bring up various weird and wonderful
> logics.
>
> Or upwards to higher-order logic, although I don't know if
> incompleteness becomes an issue then. Maybe because we are always
> dealing with unbounded but finite systems it doesn't apply or something.
> I think if you go this route you end up with things like Datalog or
Prolog.
Prolog is not higher-order logic.
And first order logic is "incomplete" also because of the "in all models"
stuff.
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