Re: If you were to implement the original relation algebra language...
From: Amund Trovåg <amundAndHereEndethMyName_at_removeINOLIKESPAMYOUSEEtexassibir.com>
Date: Fri, 21 Nov 2003 03:12:39 +0100
Message-ID: <3FBD7497.20405_at_removeINOLIKESPAMYOUSEEtexassibir.com>
> <amundAndHereEndethMyName_at_removeINOLIKESPAMYOUSEEtexassibir.com> wrote in
> message
>
> selection.
>
>
> Have you considered properties like associativity, distributivity,
> transitivity etc. ?
Yes, those properties must be properly implemented, thanks for that.
>
>
> 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...
Haha, good one!
> URL:http://www.cs.rochester.edu/users/faculty/nelson/courses/csc_173/relatio
> ns/algebra.html
>
>
>
> "project and "union" are symbols.
Yes, well, I guess you could say that. I was referring to the pi and sigma symbols that
sometimes referred to in textbooks on the relational model and thought you would understand what I meant.
Date: Fri, 21 Nov 2003 03:12:39 +0100
Message-ID: <3FBD7497.20405_at_removeINOLIKESPAMYOUSEEtexassibir.com>
Bob Badour wrote:
> "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. ?
Yes, those properties must be properly implemented, thanks for that.
> In the end though, precedence is just a convention with
> little real importance.
Could have importance when implementing it though. Even Date says that
project should have the higher precedence in RA in Introduction to DB, 2003.
>
>
>
>>>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...
Haha, good one!
>
>
>
>>>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.
Yes, well, I guess you could say that. I was referring to the pi and sigma symbols that
sometimes referred to in textbooks on the relational model and thought you would understand what I meant.
Sincerely
Amund
Received on Fri Nov 21 2003 - 03:12:39 CET