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

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Sun, 20 Nov 2005 11:45:39 +0100
Message-ID: <4380531c$0$11064$e4fe514c@news.xs4all.nl>


JOG wrote:
> Even hearing the word "null" is starting to sound embarrassing now,
> never mind postulating a definition for it. Surely the field has
> reached the point where we all know there are better ways of handling
> missing data, but given the tech we have when we get up tomorrow, and
> the job at hand, we have to make do. What more is there to say.

[Null] is a very misunderstanding prone theme, so it is ideal for the c.d.t. glossary. I wondered if this thread has brought some new insights concerning how to deal with those misunderstandings.

This is the current entry for [Null] in the c.d.t. gossary:

> [NULL]
> Roughly: a special marker that can be put in a place
> inside a data structure where an actual value is expected.
> Precisely what that marker means varies and there are at
> least three possibilities that are sometimes assumed:
>
> (1) "Unknown value" This means that on the place of the marker
> there should actually be a value but this value is not known
> at the present time. For example, if a 'name' field in a tuple
> describing a person is 'null' then this person will have a
> name but we don't know it.
>
> (2) "Absent value" This means that the property that is
> described by the value in question is simply not defined.
> For example, if the 'shipping-date' field in a tuple
> describing an order is 'null' then the order was
> not shipped yet.
>
> (3) "Whatever SQL says it means" The exact meaning is hard to
> summarize briefly, but is a mixture of the previous two
> interpretations and involves a value with three truth-values
> ('true', 'false' and 'unknown').

You have all really thought about how to talk about null. Are there reasons to change the entry? Received on Sun Nov 20 2005 - 04:45:39 CST

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