Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?

"Jan Hidders" <hidders_at_REMOVE.THIS.ua.ac.be> wrote in message news:3e4ad2b8.0_at_news.ruca.ua.ac.be...
> Lauri Pietarinen wrote:
> >
> >what is your take on Garcia-Molina, Ullman and Jennifer Widom
> >regarding their stand on duplicates?
> >
> >(see http://www.dbdebunk.com/cjddtdt.htm and cjddtdt2)
> >

[snipped for brevity]
>
> But how your algebra looks depends on how you
> answer question 2, because query optimization is the main raison d'etre of
> the algebra, and there it is a completely different story. It can for
> example be more efficient to postpone duplicate elimination. If you don't
> have a bag algebra you cannot express this in your algebra.
>

I'll try not to sound too ignorant, but I'm afraid I will anyway, as I haven't had time to read the link to Mr. Date's comments yet.

Why does query optimization have to expose bag algebra? Can't structures be manipulated at a lower internal representation that is independent of a logical data model and logical manipulative aspects (e.g. relational model with relational algebra)? Isn't this the point of ANSI-SPARC architecture? I wonder what the ramifications are on data independence if relations, whether base, derived, or intermediate, are allowed to incorporate bags in order to accomodate optimization.

Regards,

• Dan

> Note that in the writings you mention Date only addresses the first
> question, where what you actually asked concerned mostly the second
> question.
>
> -- Jan Hidders
>
>
Received on Thu Feb 13 2003 - 17:14:54 CST