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

From: paul c <toledobythesea_at_oohay.ac>
Date: Thu, 06 Apr 2006 23:27:26 GMT
Message-ID: <ythZf.3107$nf7.1228@pd7tw1no>

David Cressey wrote:
> "dawn" <dawnwolthuis_at_gmail.com> wrote in message
> ...

>>
>>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.
> However, if attributes are expressed in the form of a list, as they are in
> mathematics when discussing relations, then the mapping between attributes
> and values is based on position in the list.
>
> However, that was not Codd's point.
>
> 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.
> ...

Plus, I think, that the numbers would "change" after relops were applied (they do in Codd's examples). Maybe this is what "x" had in mind - kind of like the system doing the rename for you, the price being that you can't guess what the new "names" are going to be!

p Received on Thu Apr 06 2006 - 18:27:26 CDT