Re: So what's null then if it's not nothing?
Date: 10 Dec 2005 09:16:25 -0800
Message-ID: <1134234985.112008.177390_at_g47g2000cwa.googlegroups.com>
JOG wrote:
> vc wrote:
> > 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).
> >
> > I do not understand what exactly you are trying to say. Is it that
> > you cannot have a logic with more than two truth values ? That's
> > clearly wrong. What exactly does "3VL, which obviously can be
> > effective with more valid domains" mean ?
>
> Well, you answer your question when you quote me. Of course you can
> have 3VL. It just makes no sense with this domain. If I have {T, F, X},
> well fine, but if one then defines X as representing a lack of
> knowledge concerning T or F, the domain no longer makes sense.
> X is
> describing the state of the other values - it is part of a
> meta-theorem, and has no place sitting next to T and F.
This does not make any sense.
>(One might want
> to analogise with quantifiers in second and third order logic).
>> > You cannot because the Bollean domain does not include anything but
> >
> > > In a boolean
> > > column for example you could not place true, false and Null in a
> > > mathematically consistent system.
> >
> > {true, false}.
>
> no, you are correct. Calling it a Boolean column is silly. A column
> with a domain {True, False and Null} is what was meant, as discussed
> above.
>> > This, I do not understand. Interpretation of truth values is
> >
> > >(i.e. it necessarily requires human's
> > > to interpret the inconsistency in the practical world)
> >
> > irrelevant for the logical system to be possible.
>
> No you can't just stick any old values into a logical system. 3VL will
> obviously always work if you are thinking in terms of the symbols (that
> is how it is defined after all), but we are not dealing with things
> from a "formalist" standpoint here (bottom up).
>We already have the
> meaning of null established and are attempting to work down (a
> "realist" or "platonist" standpoint), and as such we cannot just squash
> its characteristics into a symbol and expect everything to work, just
> because we've written down a truth table.
>> > But, that's what I've been objectiong to myself in my lengthy dialog
> >
> >
> > >
> > > >
> > > > > 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.
> >
> > with Jon, right ?
>
> Sure! It looks like we are just agreeing loudly. Perhaps it looked like
> I was arguing against you, but this was not the intention. Rather I was
> just making statements, sparked off by your comments
OK.
.
>> >
> >
> > >
> > > > >. 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.
> >
> > That does not make any sense. Could you please elaborate on 'null
> > talking about underlying algebra' ?
> >
> > >As such it is the next mathematical layer, part of a meta
> > > language _about_ that level beneath it.
> > See above.
>
> Well I've maybe explained this above. Null means we do not have a value
> for boolean X say, whereas True and False are actually instances of
> those values, that Null describes are missing.
>Null is acting at a
> different level, as it describes an underlying theorem rather than
> being part of one.
The above still does not make sense.
> Now I understand my descriptions probably make this
> clear as mud, but this sort of consideration of theorems and
> meta-theorems and meta-meta-theorems is pretty much all modern
> mathematics is about (consider Godel's work).
>I do not teach this stuff
> (as you can probably tell) so all I can do is point you in the
> direction of the references I made before.
>
> All best, Jim.
Received on Sat Dec 10 2005 - 18:16:25 CET