Bill, (01)
Comments below. (02)
Leo (03)
-----Original Message-----
From: uos-convene-bounces@xxxxxxxxxxxxxxxx
[mailto:uos-convene-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Bill
Andersen
Sent: Saturday, March 04, 2006 3:48 PM
To: Upper Ontology Summit convention
Subject: Re: [uos-convene] KBR vs SQL (04)
One minor quibble, Leo... (05)
> What "larger ontology-based systems"? Which ones do you have in
> mind? What precisely do these systems do? I'm getting the feeling
> that you're talking about something very comprehensive like Cyc...
>
> LEO: No, what he is talking about is a semantic level that relational
> databases don't currently have. (06)
You subtly switched from talking about the E-R model to talking about
relational databases. I believe, for example, that Oracle's PL-SQL is
computationally complete, making it strictly as powerful as FOL. Thus, (07)
the relational *database* could be as powerful a *system* as one based
explicitly on logic, while E-R cannot be as powerul a *logic* as even
RDFS. Of course, that's not a practical comparison, but we should be
careful in our wording (goes for me too ... in spades). (08)
LEO: No, I was addressing distinct points in the prior email. I don't
know anything about Oracle's PL-SQL. I do know about SQL. There has
always been this little dance about the relational calculus, relational
databases, and FOL: is the relational calculus equiv. to FOL? Ok, in
what way? I still recall reading Reiter's "Towards a Logical
Reconstruction of Relational Database Theory" many moons ago, and
recall thinking: you mean there's some discrepancy? And though his
paper dealt with a proof-theoretical analysis, part of that proposed
extending the relational model to include more real world semantics. If
the expressivity was already there, why the need to extend it? His
point, among others, was that relational databases could be viewed as
special kinds of FO theories. And in fact Reiter makes the point that
implementation is often confused with specification. So to me, the
relational calculus has not been equivalent to FOL. (09)
.bill
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