Re: MV Keys

Jon Heggland wrote:
[...]
> No. The relation R is a predicate with three variables. A tuple is a
> variable binding that makes the predicate evaluate to true.

That is not correct (neither is). In casual speech one can mix 'redicate' and 'relation', but when one tries to be more or less precise about that sort of thing, the notions should not be confused.

>
> Of course, this is by some definition (a common one, I believe---but
> perhaps not universally accepted?), so you could claim that your
> definition is better---but I don't think it is. For one thing, it runs
> into trouble the moment you introduce more tuples: If one tuple means
> (among other things) that "A has value 3" is a fact, and another claims
> that "A has value 5" is a fact, don't they contradict each other?
>
> > The
> > tuple itself also has a truth value, "A has value 3 and B has value 7 and C
> > has value 2." which is a proposition in conjunctive normal form.
>
> No, a tuple by itself is not a fact either. Only within the context of a
> relation does it make sense to talk about facts.
>
> > The problem is that the widgit list domain is a set of lists of widgits,
> > which can be constructed using the combinatorial rules. Some of the
> > constructed lists may not violate the constraints, so the meanings overlap.
> > This is not true of the use of integers in multiple places, because integers
> > describe one aspect of a domain, they're not the domain.
>
> I'm not able to make much sense of that, and I'm still not completely
> clear on what combinatorial rules are. Can you make a concrete example
> of widgit lists that shows the problems you imagine?
> --
> Jon
Received on Wed Mar 08 2006 - 14:26:52 CET