Re: Is relational theory irrelevant? (was Re: Dreaming About Redesigning SQL)

"Thomas Favier" <tom-N-O_at_S-P-A-M-blg.fr> wrote in message news:bos71q$ugv$1_at_news-reader3.wanadoo.fr...
> Mikito Harakiri wrote:
> > Ordering is legitimate mathematical construct. It is a question, though,
if
> > one can have a simple algebra/calculus that would include ordering too.
>
> For what i can remember from my math lectures, ordering is defined by a
> relation (math meaning) between members of a set. So in relationnal
> terms, an order on a relation is another relation that lists all couples
> of the relation that are linked by the order operator.
> You can choose to implement it either by giving the full list of couples
> or by defining the operator. Both of those methods are external to the
> relation.
>
> The queries you are giving are using an order operator defined on the
> domain of one of the attribute to implicitely define the "order
> relation" on the relation.
>
> So, the relationnal algebra already permits to express ordering. I agree
> with Bob's "Relations have no order", but i do not attach it at the
> physical level.

Relations have no order. The values in relations have order. An ordered structure, like an array for instance, involves physical order. Received on Wed Nov 12 2003 - 16:15:28 CET