Re: Proposal: 6NF
Date: Thu, 05 Oct 2006 23:59:03 +0200
Message-ID: <rqvai2pjriqh2hpdqt95kunfit0voq2ibt_at_4ax.com>
On Fri, 6 Oct 2006 00:21:17 +0300, Sampo Syreeni wrote:
>On 2006-10-05, Bob Badour wrote:
>
>> So, you are saying that laying zero eggs includes the inapplicability
>> of the whole concept of laying anything. If zero suffices, why NULL?
>
>Because a bird that has laid zero eggs might then be observed to lay
>more, and we would want to assign a nonzero value to its eggs_laid. With
>camels it's different.
Hi Sampo,
So basically you are saying that you want to store the fact that a bird is able to lay eggs and a camel is not. A proposition such as
"<Birdtype> is <YesOrNo> able to lay eggs."
Don't try to make NULL mean "there may not be a value here" - it doesn't mean that. The *only* meaning NULL has is "value is missing". If you are interested in the reason why a value is missing, you should model a proposition to store that reason.
Best, Hugo Received on Thu Oct 05 2006 - 23:59:03 CEST