Re: Does Codd's view of a relational database differ from that of Date & Darwin? [M.Gittens]

From: FrankHamersley <FrankHamersleyZat_at_hotmail.com>
Date: Mon, 06 Jun 2005 12:55:36 GMT
Message-ID: <cJXoe.4372$F7.3008@news-server.bigpond.net.au>

Paul wrote:

> mountain man wrote:

>>According to this reference we can replace a null in the salary
>>field with "Salary not known" and/or "Unsalaried". This has
>>taken some work to do, by a database professional, to derive
>>an "improved" version of the personnel table (when needed).
>>
>>So what? The original design schema is simply missing information
>>for these elements, and this information needs to be entered,
>>and/or determined and entered.

> 
> If you replaced both "Salary unknown" and "Unsalaried" with NULLs, how
> do you distinguish between the two?

Without redressing the fundamental weaknesses in the schema you can't.

However I remain to be convinced that the domain "overloading" used to underpin Date's example is a useful contribution to the state of the art. Frankly my first impression was to see it as justifying a steaming hot pile! There are no signs of any elegance regardless of how unsatisfactory that is to purists, although I expect Date would cite the limitations of the current technologies as largely responsible for the latent ugliness of the "null-less solution".

Personally I see the better solution within the context of this thread is to have a discrete attribute with a domain of "Salaried, Unsalaried".   The argument about to null or not to null (sic) is for another time.

Felicitations to all,
Frank. Received on Mon Jun 06 2005 - 07:55:36 CDT