Re: A simple notation, again

From: paul c <toledobythesea_at_oohay.ac>
Date: Thu, 19 Jul 2007 01:48:47 GMT
Message-ID: <3qzni.130501$NV3.628@pd7urf2no>

Cimode wrote:
> On 17 juil, 15:57, paul c <toledobythe..._at_oohay.ac> wrote:
>

>>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
>
> R1 = {("David", "Cressey", 1), ("Jan", "Hidders", 4)}
> <>
> R2 = {("David", "Cressey", 1), ("Hidders", "Jan", 4)}
>
> --> because if an ordered header H1 = {("FirstName", "Last",
> "Number")} is associated to the definition of R1 AND because H1 is
> necessarily ordered...
> ...

I think the ordering dependence Codd had in mind doesn't have to do with   the nature of sets, rather the internal organization and the external   presentation of relations, or even tables and the operations a system supports. Date said something like users shouldn't be forced to use a single pre-defined ordering and that's what I think Codd was after. I think he simply wanted

R1:
A
1
2

and

R2:
B
2
1

to be equal as far as his calculus and algebra were concerned.

And (I think) he wanted to make sure that any representation of a relation, such as "tables" wouldn't depend on column ordering, which is why he wanted to take names of "columns" out of programs and put them in the db.

For myself, being a sloppy typist (and writer, ha, ha) I usually want a system to treat Magoo, magoo and MAGOO as equal and I'm usually quite happy if *I* can pre-define all domains to treat those as the same, tables to not show them as different. So I might see "Cimode" in my table and if I then try to insert "CIMODE", the system might fold the value into upper case and just to please me, show "CIMODE". But that's only because I told the system in advance to do things that way, not because its algebra depends on that arrangement.

So, I can be certain that my single-user system pleases me and doesn't base its decisions on somebody else's idea of what is proper ordering.

Actually, I think it is a fairly minor point of Codd's, he just wanted to make sure that ordering could not change the information in an answer, which I would have thought would be a natural consideration for any thoughtful developer. As much as I criticize SQL (which I think is easy even if I don't know it much!), I don't see anything wrong with "ORDER BY". p Received on Wed Jul 18 2007 - 20:48:47 CDT