Re: NULLs: theoretical problems?

On 21 aug, 17:19, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:
> Jan Hidders <hidd..._at_gmail.com> wrote innews:1187699645.789970.23980_at_57g2000hsv.googlegroups.com:
>
>
>
> > On 21 aug, 01:13, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:
> >> Jan Hidders <hidd..._at_gmail.com> wrote
> >> innews:1187645998.798282.58960_at_g4g2000hsf.googlegroups.com:
>
> >> > On 20 aug, 17:14, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:
> >> >> Jan Hidders <hidd..._at_gmail.com> wrote in
> >> >> news:1187599195.269472.153110 _at_a39g2000hsc.googlegroups.com:
>
> >> >> > On 20 aug, 01:48, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:
> >> >> >> I wonder what the truth tables for 'AND' and 'OR' would look
> >> >> >> like with the DEF operator. Could you show those tables ?
>
> >> >> > They would be the usual table you already gave:
>
> >> >> >> x y AND
> >> >> >> -------
> >> >> >> defined
> >> >> >> 0 0 0
> >> >> >> 1 0 0
> >> >> >> 0 1 0
> >> >> >> 1 1 1
>
> >> >> What is 'x AND y' equal to if x is '1' and y is not defined ?
>
> >> > The database would not allow you to write that. If y is nullable
> >> > then it forces you to write "DEF y : x AND y".
>
> >> What is DEF y : x AND y equal to if x is '1' and y is not defined ?
>
> > False. Because DEF y : f(y) means that (1) y is defined and (2) f(y)
> > holds.
>
> So you convert undefined operands in your logical formulas to 'false'.

No. There is no conversion necessary. That's the whole point.   

• Jan Hidders