Re: database design method
Date: Mon, 11 Nov 2002 22:10:18 -0500
Message-ID: <nl_z9.303$pV4.163278957_at_radon.golden.net>
"Jan Hidders" <hidders_at_REMOVE.THIS.uia.ua.ac.be> wrote in message
news:3dd011dd$1_at_news.uia.ac.be...
> D Guntermann wrote:
> >
> >Moreover, Mr. Date, in chapter 11, does go on to say that it seems
> >prefereable to avoid relation-valued attributes, at least for base
relation
> >variables in most cases, because they are asymmetric and provide a degree
> >of needless complexity.
>
> I fully agree with Date here. In fact, I would even go further then that.
> IMO we should stick with the original flat interpretation of the
relational
> model, (so not even relation-valued attributes) but with the addition that
> we allow domains of abstract identifiers (or object identifiers if you
want
> to call them that).
With user defined types, one can define whatever type one wants. If you want
a type to use as an abstract identifier, just define one. Ordered, unordered
whatever you want. Just tell the DBMS what operations it has.
> People often forget that the requirement that the domains
> should not contain abstract identifiers is something where the relational
> model deviates from first-order logic.
How so? The relational model allows full support of user defined types.
> But perhaps one of these days Date will explain to use that this is what
> Codd had meant all along. :-)
Perhaps, one day.
> -- Jan Hidders
Received on Tue Nov 12 2002 - 04:10:18 CET