Re: So what's null then if it's not nothing?

On 17 Nov 2005 03:39:01 -0800, JOG wrote:

>I think nulls may have been done to death in the literature. Date,
>Darwen and Pascal have written reams on the matter (and convincingly so
>- I don't think anyone would argue they are theoretically correct, just
>whether practically it matters). The problems all arise from english,
>and how we formulate sentences. Consider:
>
>A) The dog's colour is black
>B) The dog's colour is unknown

Hi JOG,

This has nothing to do with Null. Null can't be used to represent the fact "The dog's colour is unknown". You should represent that by adding an extra column. (And I'm sure that some programmers would consider allowing "unknown" in the domain of colors -- but YUCK).

A good example for Null would be:

1. The dog's colour is black B)

In example B, no information at all is given about the dog's colour. But in a tabular format, much of the sentence is implied by the format and column heading - only the actual value is noted. That's where the problems arise, because one could then be tempted to reconstruct the sentences from the table - and one would arrive at

A') The dog's colour is black
B') The dog's colour is

And that is where most people are tempted to finish the sentence with "unknown" - but there's no guarantee that they are right when they do so.

Best, Hugo

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