Re: By The Dawn's Normal Light

"Paul" <paul_at_test.com> wrote in message news:41823114$0$33603$ed2619ec_at_ptn-nntp-reader02.plus.net...
> Dawn M. Wolthuis wrote:
> >>It can if you want it to; I can certainly understand a DBMS vendor
> >>offering lists as a built-in type. But it's not important for the DBMS
> >>to know any more about the List than about the Set or the Date or
> >>the... offering them would just be a convenience. It doesn't affect
> >>relational theory or practice.
> >
> > I agree that the database need not know more about a List or Set than
about
> > a Date, but why does it need to know more about a Relation than about a
> > List? Thanks. --dawn
>
> Because a relation represents a logical predicate, and that is the
> fundamental part of a DBMS. And a collection of propositions don't have
> any intrinsic order, so they just need to be a set, not a list. The
> ability to have columns/values of different types is just the icing on
> the cake.

Where ordered lists are not implemented, users place ordering attributes into the data. The predicates stay the same whether a user adds in an ordering attribute or the dbms software handles the ordering attribute (along with inserts & deletes to an ordered list). There is no change to predicates in this case. --dawn Received on Fri Oct 29 2004 - 14:56:13 CEST