Re: So what's null then if it's not nothing?
Date: 29 Nov 2005 08:16:32 -0800
Message-ID: <1133280992.421387.165640_at_g44g2000cwa.googlegroups.com>
Jon Heggland wrote:
> In article <1133272410.483257.280890_at_o13g2000cwo.googlegroups.com>,
> boston103_at_hotmail.com says...
[...]
> > With respect to nulls, SQL is no more confused that Codd's original
> > work on which SQL's null treatment is based. There is no need to
> > attack SQL whose deficiencies are well known if all one wants to
> > discuss is the notion of null..
>
> Then consider my statement an attack on Codd, if SQL is faithful to his
> work. Alternatively, tell me how SQL is deficient with respect to Codd.
Most notably, SQL deviates from the 3vl with respect to EXIST.
>
> > > > Whether or not two values are considered distinct is irrelevant to the
> > > > null = null comparison.
> > >
> > > By SQL fiat, perhaps. But *should* it be? What gives SQL the right to
> > > redefine notions of equality and "distinctness" in this manner? Or never
> > > mind the right; does it make *sense*? Is it worth the price?
> >
> > null=null evaluates to unknown according to the 3vl logic rules.
>
> 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".
He did not invent the 3VL, there had been Lukasiewicz before.
>
> > Again, SQL per se does not have much to do with the notion of null.
> > Please see Codd's article I mentioned earlier and comment on it rather
> > that criticizing SQL.
>
> Isn't it pretty much the same? Again, please tell me what you consider
> the deficiencies of SQL.
See above.
>
> As for Codd's article, I think it is a bad idea in itself to use 3VL.
> Codd himself admits it produces seemingly paradoxical results and breaks
> what we expect to be tautologies. Also, to conflate the unknown truth
> value with null seems like a huge blunder. Finally, he discusses the
> RM's relationship to predicate logic, but fails completely to consider
> the effects of nulls on this relationship.
> --
> Jon
Received on Tue Nov 29 2005 - 17:16:32 CET