Re: If you were to implement the original relation algebra language...

"Amund Trovåg"
<amundAndHereEndethMyName_at_removeINOLIKESPAMYOUSEEtexassibir.com> wrote in message news:3FBD2223.5000107_at_removeINOLIKESPAMYOUSEEtexassibir.com...
>
> Joe \"Nuke Me Xemu\" Foster wrote:
> > "Amund Trovåg"
<amundAndHereEndethMyName_at_removeINOLIKESPAMYOUSEEtexassibir.com> wrote in message
> > <news:3FBD12DB.40205_at_removeINOLIKESPAMYOUSEEtexassibir.com>...
> >
> >
> >>Would precedence have a lot to say for optimization?
> >>
> >>I am currently working on doing just this, creating the grammar file
> >>from BNF to JavaCC(a program that makes Java parser files for me, based
> >>on a grammar).
> >>
> >>I am not certain whether project should have precedence over the other
> >>operators, as this might create trouble when combined with e.g.
selection.
> >>
> >>Any thoughts, comments or tips on how the grammar should be structured
> >>with regard to this?

Have you considered properties like associativity, distributivity, transitivity etc. ? In the end though, precedence is just a convention with little real importance.

> > Punt and require parentheses?
> What does punt mean? Pardon my english here...

Please excuse Mr. Foster. He is making reference to a move in football that signifies desperation. And no, I don't mean that sissy game played in Europe where a bunch of boys in short pants and long stockings bounce balls off their heads. I mean that homophobic American game where oversized steroid abusers pile on top of each other but with sufficient padding to prevent any suggestion of male-male contact.

Then again, I seem to recall George Carlin suggested the latter game was the european game. Hmmm...

> > It shouldn't impede optimization, and
> > a functional notation for those of us with "standard" keyboards will
> > all but demand it:
> >
URL:http://www.cs.rochester.edu/users/faculty/nelson/courses/csc_173/relatio ns/algebra.html
> >
> > You might be able to get away with R1 + R2 for union, R1 - R2 for
> > set difference, R1 * R2 for kernel panic: out of swap, etc., but you
> > should encourage parentheses here too, because R1 - (R1 - R2) isn't
> > the same as (R1 - R1) - R2.
>
> Yeah you got a point there. Association must be looked at when deciding
> for parentheses.
> I am actually going to allow the user to say "project" "union" etc,
> instead of using symbols...

"project and "union" are symbols. Received on Fri Nov 21 2003 - 01:44:24 CET