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

"Jan Hidders" <jan.hidders_at_REMOVE.THIS.ua.ac.be> wrote in message news:3e6da66b.0_at_news.ruca.ua.ac.be...
> Lauri Pietarinen wrote:
> >Jan Hidders wrote:
> >>Lauri Pietarinen wrote:
> >>>
> >>>I was not really trying to impress you by those references. I was just
> >>>figuring that since we were talking about aggregates we should have
some
> >>>reference (if not agreement) as to what an aggregate function means.
> >>
> >>Why do you think there is disagreement about that?
> >>
> >Well, from reading those articles by Date I don't get the impression that
> >bags provide more optimisations than sets regarding aggregates as you
> >suggested.
>
> The "that" in my sentence referred to your "what an aggregate function
means".
> I'm curious why you think that the meaning of the term is controversial.
>
> >>>Regarding point 5) I challenge you to give me just
> >>>*one* *real* *world* *example* in which duplicates
> >>>would actually be of use to the end user.
> >>
> >>I never said there was, and even if there was you could simulate this in
a
> >>set-only model.
> >>
> >>So, what is your point exactly?
> >>
> >If nobody needs them (bags) why support them? Even if the cost is zero?
>
> I'm not convinced that bags are never needed. There's a reason that
> mathematicians introduced it; they needed it to model certain things. What
> about Petri nets, for example? And if you are then going to simulate them
> with sets then the cost might become negative because the set-based
> optimizer might miss certain optimizations that would have been easier to
> spot for a bag-based optimizer.

Such as? Received on Tue Mar 11 2003 - 16:56:40 CET