Re: Interpretation of Relations
Date: 23 Jan 2007 06:00:23 -0800
Message-ID: <1169560823.328712.226600_at_q2g2000cwa.googlegroups.com>
Joe Thurbon wrote:
>
> Depending on how you interpret relations into predicates, I would say
> that JOIN and PROJECT are kinds of inferencing rules. But they seem
> quite different to modus ponens.
They have got nothing to do with modus ponens and certainly are not
inference rules.
The simplest way to see that RA is a subset of FOL is to rewrite RA
expressions as Horn clauses:
Natural join: nj(X,Y,Z) <- r1(X,Y), r2(Y,Z).
Projection: proj(X) <- r1(X, Y). Selection: sel(X,Y) <- r1(X, 123).
> I have other questions, too, of course. What does it mean to close a
> set of relations under consequence? (Is is the repeated application of
> JOIN and PROJECT?)
>What is the analog of, say, material implication?
The usual.
> What is a valid implication?
What's your definition of a "valid implication" ?
>
> What parts of logical consequence do I
> lose when I represent my knowledge in a relational form.
What's your definition of logical consequence ? Received on Tue Jan 23 2007 - 15:00:23 CET