Re: Proposal: 6NF

Brian Selzer wrote:
> "JOG" <jog_at_cs.nott.ac.uk> wrote in message
> news:1159954091.119164.155490_at_m73g2000cwd.googlegroups.com...
> > All of your points represent a wild goose chase in my eyes Brian. A
> > proposition with a NULL in it is no proposition at all. From a logical
> > perspective, case closed. A relation tuple with a NULL in it is no
> > relation tuple at all. From a mathematical perspective, case closed.
> > Trying to invoke the 'kludge perspective' is hardly going to convince a
> > theoretical newsgroup.
> >
>
> Is the empty set a value? Yes, it is. So why can't a null be?

Because an empty set is a value and a NULL is not.

>
> By your reasoning, a proposition with an integer in it is no proposition at
> all; a proposition with a string in it is no proposition at all; a
> proposition with a widgit in it is no proposition at all.

poppycock. Those are all fine propositions.

>
> Also, haven't you heard of the existential quantifier?

Not in a proposition of fact, absolutely not.

This has been explained many times now. A null _indicates_ that there is a missing/unknown/inapplicable value, it is not a value itself. A proposition with a missing/unknown/inapplicable hole is not a proposition.

> For example, if a
> schema {X, Y, Z} has X as a key and Z can be null, then the sentence
>
> EXISTS x (P(x) XOR Q(x))
>
> where P is defined in terms of X and Y and where Q is defined in terms of
> X, Y, and Z is a perfectly valid construct in FOPL.
Received on Wed Oct 04 2006 - 15:59:46 CEST