Re: A simple notation, again
Date: Wed, 18 Jul 2007 11:59:05 -0700
Message-ID: <1184785145.523735.182430_at_i38g2000prf.googlegroups.com>
On 17 juil, 15:57, paul c <toledobythe..._at_oohay.ac> wrote:
R1 = {("David", "Cressey", 1), ("Jan", "Hidders", 4)}
<>
--> because if an ordered header H1 = {("FirstName", "Last",
"Number")} is associated to the definition of R1 AND because H1 is
necessarily ordered...
> Cimode wrote:
> > On Jul 16, 7:05 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:
>
> >>"David Cressey" <cresse..._at_verizon.net> wrote in message
>
> ...
>
> >>How about something like this
> >>{(Last, First, Num) :
> >>("David", "Cressey", 1),
> >>("Marshall", "Spight", 2),
> >>("Bob", "Badour", 3),
> >>("Jan", "Hidders", 4)}
>
> > You imply order (adjacency) when relation attributes should not be
> > subjected to any....
>
> When Codd wrote of eliminating order dependency, he wasn't talking about
> language notations or grammars, in fact he used ordering to describe his
> idea!
Thank you for pointing that out. I was ranting on something I never
totally felt comfortable with. To remain coherent with the unordered
nature of sets, I always felt frustrated that representing *grammar*
of a relation would be otherwise than by *not* assuming order. I
thrust it becomes imperative when representing relation as tables and/
or because we include the header as part of relation definition. In
other words why
R2 = {("David", "Cressey", 1), ("Hidders", "Jan", 4)}
As I have not found anything better to propose, just ignore my comment...
> p
Received on Wed Jul 18 2007 - 20:59:05 CEST