Re: So what's null then if it's not nothing?
Date: 9 Dec 2005 07:18:31 -0800
Message-ID: <1134141511.458603.73950_at_g44g2000cwa.googlegroups.com>
JOG wrote:
> vc wrote:
> > JOG wrote:
> > > vc wrote:
> > > > Jon Heggland wrote:
> > > > > In article <1134052742.347560.142840_at_o13g2000cwo.googlegroups.com>,
> > > > > boston103_at_hotmail.com says...
> > > > > >
> > > > > > > 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.
> > > > >
> > > > > It does *not* include such a value. NULL is not a truth value any more
> > > > > than it is a number or a string.
> > > >
> > > > I am missing something. If you store/use NULL as a logical value, haw
> > > > can it *not* belong to the logical vaue domain with its logical
> > > > operations? Sorry, but that does not make sense.
> > > [snip]
> > >
> > > But Null can never _be_ a logical value: it is by definition an
> > > indicator of the very absence of a logical value. In addition, as a
> > > logical value how could it possibly exist?
> >
> > I am not sure what point you are trying to make. Are you suggesting
> > that nulls be allowed in , say, Boolean columns ? Or just the opposite
> > ?
>
> That you cannot mathematically incorporate the null concept into a
> logical system in the way that has been proposed (i.e. 3VL, which
> obviously can be effective with more valid domains).
> In a boolean
> column for example you could not place true, false and Null in a
> mathematically consistent system.
You cannot because the Bollean domain does not include anything but {true, false}.
>(i.e. it necessarily requires human's
> to interpret the inconsistency in the practical world)
>> >
> >
> > > In a world where the equality relation over a logical domain is not reflexive?!? This whole
> > > argument makes no sense to me.
> > Whose argument are you objecting to ?
>
> The argument that would incorportate Null != Null into the logical
> arrangement - this would mean that the equality relation in the domain
> would be non-reflexive, a nonsense in a logic system. This should be
> the stopping point for that train of thought imo.
But, that's what I've been objectiong to myself in my lengthy dialog with Jon, right ?
>> >
> > >. If you want to use nulls, well
> > > mathematically your looking at a meta-language, and you simply can not
> > > condense it all down into a single conceptual level (Or hofstadter
> > > might point out that you have to pass it up to the next djinn!).
> > What's that supposed to mean ?
>
> That mathematical levels are being confused in this discussion (a very
> easy thing to do). Null talks about the underlying algebra - it is not
> part of it.
>As such it is the next mathematical layer, part of a meta
> language _about_ that level beneath it.
See above.
>You must not try to squash them
> in together. I recommend having a look at the development of set theory
> from naive to modern for a better description of this sort of thing
What specific points I made are you objecting to ? Received on Fri Dec 09 2005 - 16:18:31 CET