From: David Cressey <>
Date: Sat, 05 Jan 2008 15:29:43 GMT
Message-ID: <HnNfj.482$xA6.437_at_trndny09>

"Roy Hann" <specially_at_processed.almost.meat> wrote in message
> "David Cressey" <> wrote in message
> news:VwKfj.321$vX6.267_at_trndny05...
> >
> > I disagree. A null doesn't indicate that information exists. There is
> > always the "not applicable" case
> Which, I believe, is almost invariably the reason that nullable attributes
> get introduced in real databases. I continue to be baffled at this
> preoccupation with flagging information that must exist but isn't known.
> Discuss it if you must (I absolutely don't care about it), but don't
> the more common problem.

The "not applicable" case is the one that can be obviated by normalization. That may the the reason that c.d.t. regulars treat it as unworthy of discussion.

The "not available" case is more philosophical. Even with full normalization there can be facts that the database doesn't know, and knows that it doesn't know. There can also be facts that the database doesn't know, and doesn't know that it doesn't know. In my mind, this case has more to do with the nature of knowledge itself than with the theory of databases. But, for some reason, it never fails to attract the same discussion every time the topic comes up. Received on Sat Jan 05 2008 - 16:29:43 CET

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