From: Dawn M. Wolthuis <dwolt_at_tincat-group.comREMOVE>
Date: Fri, 1 Oct 2004 17:59:35 -0500
Message-ID: <cjkngs$dgr$>

"mAsterdam" <> wrote in message news:415c9c59$0$78738$
> Sorry for changing the subject line.
> This is not glossary stuff, I think
> it's worth discussing in its own right.
> Dawn M. Wolthuis wrote:
> > mAsterdam quoted:
> >>Confusion arises when people use terms like "null value",
> >>a paradox to some, a contradictio in terminis to others.
> >
> > And to others a perfectly useful concept.
> Very useful, definitely. It's use would not have
> become so widely spread otherwise.
> "perfectly" - I don't think so.
> "concept" - or filler for the lack of one.

You called me on that one -- what was I thinking? I think I intended that it was a "perfectly useful value" and stopped thinking before I finished typing. Sorry.

> > This depends more on your
> > database implementation than on the theory.
> Implementors have to deliver.
> If somebody could shed some light
> on the early history of NULL in databases,
> I would be grateful. Pure curiosity.

I suspect that might depend on your definition of a database. If file structures count (which they should based on our glossary definition of a database) then maybe it traces to storing "low-values" from programming languages and character sets.

> > There could be relational
> > databases as well as non-relational databases that hold to null as a
> Agreed. Nuance:
> Whenever somebody (forced or not) decides to
> represent the absence of a value (s)he has
> to decide *how* (with which sign) to
> represent this absence. So there will be
> a sign, a value of some kind, to represent
> the absence of a value on another level.
> It has to be on another level, because on
> this one the dice are thrown: there *is* a value.
> Next problem: what are these levels.

Yes, a "value" is used to represent the absense of value. That is why you refer to a three-valued logic when true, false, and "no value" are the options.

Getting back to the glossary entry for NULL, the definition should reflect a different in the treatment of null based on whether it used as the "no value" value in a 3VL or is used as an "empty set" value in a 2VL. I have no hands-on experience with 4 or 5VLs and nulls (and no particular interest) but I just wanted to be sure that a 2VL was included when defining NULL.

> > SQL, on the other hand, has null as a non-value.
> Dunno. Don't care

> >>Confusion arises due to the fact that
> >>nullness (the absence of value) is often
> >>represented on computers by the number 0.
> >>(Obviously, 0 is not null.)
> >
> > The confusion arises more because some products interpret null as a
> > (especially those that employ a two-valued logic) while others, SQL in
> > particular, interpret null as a non-value although SQL is said to have a
> > three-valued logic.
> I said I don't care! (Oh well, you didn't read that
> yet when you wrote this :^)
> My daughter (13), yesterday in a conversation:
> "Don't laugh unless you think otherwise".


> >>In some contexts, 'null' and 'nil' mean the same thing;
> >>in others, they do not.
> >>
> >>In databases traditionally NULL is used and opposed.

> > In relational databases, ...
> Ok.

Or you could say in 3VL databases

> > The quotations are great. --dawn
> Credits to laconic2.

Yes, indeed. --dawn Received on Sat Oct 02 2004 - 00:59:35 CEST

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