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_at_news.xs4all.nl>
>
>
> 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.
>
>
> 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.
Date: Sat, 08 Apr 2006 02:25:57 +0200
Message-ID: <4437030e$0$11073$e4fe514c_at_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 Sat Apr 08 2006 - 02:25:57 CEST