Re: NULLs

"Marshall" <marshall.spight_at_gmail.com> wrote in message news:7dbb4504-dc08-48a1-b84f-a4c8e801aeb1_at_d4g2000prg.googlegroups.com...
> On Jan 5, 1:25 am, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> > "Marshall" <marshall.spi..._at_gmail.com> wrote in message
> >
> > > The connection between the model and what is being modeled is
> > > only in our head. We can consider the model without considering
> > > what the state of the real world is. Indeed, we can have a model
> > > that doesn't even *have* a corresponding real-world aspect. So
> > > when we talk about "missing" information, that's an attribute of
> > > the map between the model and reality in our head. It's not
> > > an aspect or an attribute of the model. At all.
> >
> > I disagree. With nulls there is an explicit indication that there is
> > information that exists but hasn't been supplied. It is not a matter of
> > interpretation. Without nulls, there is no explicit indication so it
> > becomes a matter of interpretation.
>
> The interpretation you're supplying may well be the one
> *intended* by the designers of SQL, and certainly very
> frequently used, but it definitely is *not* the only one
> possible. Furthermore we can use nulls without *any*
> interpretation. All we need is an operational semantics.
>
> Here's a relation:
>
> {(a=5, b=NULL)}
>
> Does the tuple with the b value being NULL specify that the
> b value for this tuple is missing, or does it specify inapplicable?
> Or does it specify that opening Christmas presents is nifty?
> What does b mean anyway? These questions are only sensible
> relative to a particular interpretation, and I haven't supplied one.
> And in addition to the option of supplying zero interpretations,
> I also have the possibility of supplying three, or eleven
> interpretations, each with different answers to
> the above questions.

The dog did nothing in the night.

Again. Received on Sun Jan 06 2008 - 13:03:05 CET