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

From: Jon Heggland <heggland_at_idi.ntnu.no>
Date: Tue, 29 Nov 2005 17:58:07 +0100
Message-ID: <MPG.1df6a6ff458522dc989719@news.ntnu.no>


In article <1133280992.421387.165640_at_g44g2000cwa.googlegroups.com>, boston103_at_hotmail.com says...
>
> > Indeed? Is NULL an inherent part of 3VL? Reference? I don't think Codd
> > invented 3VL ...
>
> In the Codd style 3vl it is. See the article I mentioned earlier. He
> uses w (omega) to denote NULL and his NULL is "value at present
> unknown".

Well, like I said, Codd conflates the truth value "unknown" with NULL. I'm not sure that is a good idea. In any case, I'd prefer that you say "according to Codd's 3vl rules" instead of "according to /the/ 3vl rules" (my emphasis). But you may consider that splitting hairs.

> He did not invent the 3VL, there had been Lukasiewicz before.

I am curious: In Lukasiewicz's system, what do you get when you compare the unknown truth value to itself?

> > As for Codd's article, I think it is a bad idea in itself to use 3VL.
>
> I fully agree that nulls should be avoided as much as possible,
> however, if one uses them one should understand their behavior and the
> original motivation (by Codd).

Of course. But I thought we were discussing whether Codd's nulls and rules were well designed or not. It is possible to envision alternatives.

-- 
Jon
Received on Tue Nov 29 2005 - 10:58:07 CST

Original text of this message

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