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

In article <1133280992.421387.165640@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
boston103@xxxxxxxxxxx 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
.

Relevant Pages

  • Re: So whats null then if its not nothing?
    ... >>> whereas Codd claims that it is. ... > Now, if x is missing, 3VL will evaluate the expression to unknown. ... > that the answer should be true, and that tautology recognition ought to ... >> If the first zero denotes a logical constant, ...
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  • Re: So whats null then if its not nothing?
    ... Jon Heggland wrote: ... > Well, like I said, Codd conflates the truth value "unknown" with NULL. ... >> original motivation. ...
    (comp.databases.theory)
  • Re: So whats null then if its not nothing?
    ... > the debate beween Codd and Date on the issue of nulls: ... I found no justification in the original article; ... have read the Codd/Date debate; it seems that Codd is confused about how ... > unknown value and to talk about the unknown as a logical constant as ...
    (comp.databases.theory)
  • Re: So whats null then if its not nothing?
    ... > I found no justification in the original article; ... > have read the Codd/Date debate; it seems that Codd is confused about how ... >> unknown value and to talk about the unknown as a logical constant as ... If NULL represents a 'missing value', the equality predicate over some ...
    (comp.databases.theory)
  • Re: 3vl 2vl and NULL
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