Re: Interesting article: In the Beginning: An RDBMS history
Date: 6 Apr 2006 13:08:21 -0700
Message-ID: <1144354101.878068.281070_at_z34g2000cwc.googlegroups.com>
David Cressey wrote:
> "x" <x_at_not-exists.org> wrote in message news:e12djb$ha2$1@emma.aioe.org...
> > > I don't think so. I think he was making the distinction between
> > attributes
> > > specified by name and attributes specified by position.
> >
> > What is the difference between a "name" and a "position" from a
> > mathematically point of view ?
>
> I can't speak for Codd on this, and I don't choose to speak for myself.
The only difference is the domain for the function, whether it is a set of counting numbers or a set of attribute names. If counting numbers, then there is an obvious order (function), represented as the order of a tuple.
It amuses me when people make a big deal about there being no order of the attributes in a relation (which is then not strictly a relation as Codd pointed out). Given that attributes are specified to the system in some order (create table...) and output in some order, what do I care if under the covers it knows a mapping from the counting numbers to the attribute values or from attribute names to attribute values or both?
Cheers! --dawn Received on Thu Apr 06 2006 - 22:08:21 CEST