Re: Interesting article: In the Beginning: An RDBMS history

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Sat, 08 Apr 2006 02:25:57 +0200
Message-ID: <4437030e$0$11073$e4fe514c@news.xs4all.nl>

dawn wrote:
> David Cressey wrote:

>>dawn wrote:
>>>David Cressey wrote:
>>>>x wrote:
>>>>>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.
>>
>>This is not true.
>>
>>If the numbers were explictily used as if they were names, in every place
>>where a specific attribute is specified,  your statement would be true.

>
>
> I don't see how a function being explicitly written or not makes any
> difference. In some systems you can refer to an attribute either by
> name or number. They serve as two different names for the attributes.

.... as long as the model (of the universe of discourse) does *not* change. It will.

As soon as it does change (e.g. add/scratch an attribute/column/field/whatever horizontal thingy) the /number/ references have to be re-examined whereas the /name/ simply continues to refer to the correct (as correct as it was to begin with) data.

Design principle: Look for the invariant to elicit a dependable structure.

[snip]

>>Codd's point was that users should not have to remember "names" like 23, 24,
>>25, ...etc. in order to specify attributes in a query.

>
>
> I would have to re-read things to be sure, but I thought perhaps his
> concern was over decoupling the logical and physical model of the
> attributes. In systems where attributes are referred by numbers, there
> is often a correlation between the logical and physical order, although
> there need not be.

Exegesis is not my hobby. I thought it wasn't yours either.

[snip]

>>A lot of things amuse you.
> Indeed.

:-) Received on Fri Apr 07 2006 - 19:25:57 CDT