Re: NULLS and User Input WAS Re: multimaster

On Mon, Jun 04, 2007 at 03:38:01PM +0100, Richard Huxton wrote:
> Well, a strict "unknown" is fine - so long as it means just that.
> How tall is Andrew? Unknown
> How tall is Richard? Unknown
> Are Andrew and Richard the same height? Unknown
>
> The problem is the slippery-slope from "unknown" to "not applicable" to
> "user refused to answer" to ...whatever

While you do well to point out that I have equivocated on "unknown"
(in my usual twitchy way whenever NULLs come up, I am told), your
example actually illustrates part of the problem. There are NULLs
that are actually just local absences of data (you don't know how
tall I am), NULLs that are in fact cases of 'no such data' (the full
name that 'S' stands for in Harry S Truman -- Truman's middle name
was in fact just S), NULLs that are data nobody knows (unlike the
mere locally-unknown data: "When the tree fell in the woods with
nobody around to hear it, did it make a sound?"), and NULLs that are
the data in response to questions that can't be answered, ("What
exists after the end of the universe?")

See, this is what happens when you study the wrong things in school.
You start to think that logic and metaphysics are somehow related to
one another. :-/

A

--
Andrew Sullivan | ajs(at)crankycanuck(dot)ca
The fact that technology doesn't work is no bar to success in the marketplace.
--Philip Greenspun