Re: RM and definition of relations/tuples
Date: 25 Nov 2005 06:14:48 -0800
Message-ID: <1132928088.319871.174170_at_g49g2000cwa.googlegroups.com>
Martin Zapf wrote:
[...]
> I also figured that out, a mathematical relations (subset of catesian
> product) is ordered because the elements of a cartesian product are
> ordered sets by definition.
>
> And yes I have to do some theoretical db stuff so Im asking myself:
> If there are two definitions for the same thing, what is the universal
> valid and precise definition for the RM? This two definitions cant come
> out of nowhere, can they.
As I said, the second definition is what you'd want to use. For the rationale, see Date's "Introduction to .d.b. systems" or his numerous articles on the subject.
It's just an implementation artifact that columns in a modern RDBM table are ordered (when queried). Received on Fri Nov 25 2005 - 15:14:48 CET