Re: NULLs: theoretical problems?
Date: Sat, 25 Aug 2007 11:18:02 -0000
On 25 aug, 02:09, "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
> 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 !
> the DEF logic behaves the same way as the SQL three-valued logic does in
> all the cases except (1).
- Jan Hidders