Re: NULLs: theoretical problems?

On Aug 25, 1:09 am, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:
> Jan Hidders <hidd..._at_gmail.com> wrote innews:1187998994.047351.228760_at_q4g2000prc.googlegroups.com:
>
> > On 25 aug, 01:35, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:
> >> Are you saying that 'DEF t.a : (t.a = 5 OR TRUE)' evaluates to
> >> 'false' ?
>
> > It evaluates to 'false' if t.a is undefined, and to 'true' if it is
> > defined.
>
> >> Please give us the DEF operator interpretation rules. Without the
> >> rules the discussion quickly becomes rather meaningless, really !
>
> > I've already done that twice. So for the third time: The formula "DEF
> > c : f(c)" evaluates to true if c is defined and f(c) evaluates to
> > true, and to false in all other cases.
>
> Very well. Now that we have the rules, let's consider some aspects of
> the DEF logic that I've already mentioned but do not mind repeating my
> words again:
>
> 1. The classical logic 'x or true=true' does not hold if x is undefined.
>
> 2. The classical logic 'x or not x = true' does not hold if x is
> undefined. Parenthetically, I find your complaint about the same
> phenomenon in the SQL three-valued logic, well, mysterious taking into
> account the fact that the DEF logic has the same defect !

Achilles: Look tortoise, I've been given a big bag of apples. Yum.
Tortoise: Wow thats, great. How many yellow bananas are in there?
Achilles: Eh? What sort of question is that?
Tortoise: Look, stop hogging the fruit. Do you have a yellow banana in

Achilles: [sighing] false, again I'm afraid.
Tortoise: HA! Impossible!
Achilles: What on earth are you on about!
Tortoise: I have you, you dishonest scoundrel. Everyone clearly knows

>
> To sum up, when comparing the SQL three-valued logic with the DEF-
> logic, we have a net loss of meaningfullness (see point 1) ! Apparently,
> the DEF logic behaves the same way as the SQL three-valued logic does in
> all the cases except (1). It brings us back to your original claim that
> the DEF logic is better that the SQL three-valued logic for handling
> undefined values. Am I missing something ?
>
> Please comment.
>
>
>
> > -- Jan Hidders
Received on Sat Aug 25 2007 - 03:05:58 CEST