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@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 Thu Nov 20 2003 - 20:12:39 CST