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

From: vc <boston103_at_hotmail.com>
Date: 8 Dec 2005 06:39:02 -0800
Message-ID: <1134052742.347560.142840_at_o13g2000cwo.googlegroups.com>


Jon Heggland wrote:
> In article <1133987926.307730.65450_at_g14g2000cwa.googlegroups.com>,
> boston103_at_hotmail.com says...
[...]

> > How is the crucial point
> > that distinguishes the 2VL from a multivalued logic, namely the number
> > of truth values is a non-sequitur ?
>
> I don't think a "regular" unknown/missing SQL NULL for a 2VL boolean
> domain should be regarded a truth value. That would be inconsistent with
> how NULL works in other domains.

Then the logic ceases to be such if its truth values set include a value for which the equality predicate evaluates to anything other than TRUE or FALSE as I said elsewere.

>
> > > And your conclusion is ..? That for Boolean attributes, NOT NULL must be
> > > enforced at all times?
> >
> > In order for Boolean attributes to remain such, yes, otherwise they
> > would be not Boolean and necessarily one would be using a logic other
> > than Boolean which would have much more profound implications that
> > extending the integer domain with nulls.
>
> I disagree. For consistency, I'd say that any boolean expression
> involving NULL booleans should evaluate to NULL, just like any
> arithmetic expression involving NULL integers evaluates to NULL (at
> least if you accept the excuse for how SUM() works:). I don't think it
> breaks logic more than it breaks arithmetic. If you disagree, can you
> give any examples of profound implications?

See above. You cannot determine logical expression equivalence, you have no ability to derive anything in such 'logic', what use such structure might have ?

> --
> Jon
Received on Thu Dec 08 2005 - 15:39:02 CET

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