Re: Interpretation of Relations
From: paul c <toledobythesea_at_oohay.ac>
Date: Tue, 23 Jan 2007 14:51:51 GMT
Message-ID: <bipth.793272$R63.169668_at_pd7urf1no>
>
>
> They have got nothing to do with modus ponens and certainly are not
> inference rules.
>
> The simplest way to see that RA is a subset of FOL is to rewrite RA
> expressions as Horn clauses:
>
> Natural join: nj(X,Y,Z) <- r1(X,Y), r2(Y,Z).
Date: Tue, 23 Jan 2007 14:51:51 GMT
Message-ID: <bipth.793272$R63.169668_at_pd7urf1no>
vc wrote:
> 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).
Doesn't this let us infer that there is a relation between X and Z and another between X and Y?
> Projection: proj(X) <- r1(X, Y).
Doesn't this let us infer that there is a relation between X and some Y?
> Selection: sel(X,Y) <- r1(X, 123).
I don't get this one, usually I think of selection based on natural join as in http://www.dcs.warwick.ac.uk/~hugh/TTM/APPXA.pdf
> ...
p Received on Tue Jan 23 2007 - 15:51:51 CET