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

From: D Guntermann <>
Date: Thu, 13 Feb 2003 23:14:54 GMT
Message-ID: <>

"Jan Hidders" <> wrote in message
> Lauri Pietarinen wrote:
> >
> >what is your take on Garcia-Molina, Ullman and Jennifer Widom
> >regarding their stand on duplicates?
> >
> >(see 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.


  • 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 Fri Feb 14 2003 - 00:14:54 CET

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