Re: NULL
From: Jan Hidders <jan.hidders_at_REMOVETHIS.pandora.be>
Date: Fri, 10 Jun 2005 16:27:25 GMT
Message-ID: <Nbjqe.115867$vN7.6728845_at_phobos.telenet-ops.be>
>
> Are you referring to the part about being
>
> "distinct from the empty character string
> or a string of blank characters
> and distinct from zero
> or any other number" (in Rule 3),
Date: Fri, 10 Jun 2005 16:27:25 GMT
Message-ID: <Nbjqe.115867$vN7.6728845_at_phobos.telenet-ops.be>
mountain man wrote:
> "Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote:
>> mountain main wrote: >>> >>>What is lacking Codd's concise definition (rule 3) >>>for null data as "non-applicable data"? >> >>Read closely, that is not precisely how he defines it.
>
> Are you referring to the part about being
>
> "distinct from the empty character string
> or a string of blank characters
> and distinct from zero
> or any other number" (in Rule 3),
No.
> or are you referring to Codd's work elsewhere,
> like his "Extending the DB RM ..."?
No.
I'm referring to the part of this definition that says "for representing missing information and inapplicable information". He's talking about two things, one being "missing information" and the other being "inapplicable information", that can be indicated by null values. Your summary of his definition restricts this to only one of them.
- Jan Hidders