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

From: Roy Hann <specially_at_processed.almost.meat>
Date: Sun, 20 Nov 2005 11:56:38 -0000
Message-ID: <>

"mAsterdam" <> wrote in message news:4380531c$0$11064$
> 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?

If that is all there is to it, then it definitely needs to be extended. Without implying that I approve of the three existing so-called meanings (I don't), it needs to include (at least) a fourth possibility: "meaningful value not even possible". Used when multiple dissimilar entity types are (wrongly) conflated.

Roy Received on Sun Nov 20 2005 - 12:56:38 CET

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