Re: Interpretation of Relations

Joe Thurbon wrote:
[snip]
> > As a logician perhaps you can tell me if the following makes any sense
> > - to say Joe does have a hair colour and is not bald, I'd have:
> > P = Ep Name(p, Joe) ^ Ey Hair(p, y).
> >
> > Or to say Joe is bald:
> > P = Ep Name(p, Joe) ^ ~Ey Hair(p, y).
> >
> > Or to say I don't know if I don't know if Joe is bald or not, well this
> > is inferred from not saying anything at all.
>
> Yep, this makes sense to me. I'm assuming that by "=" you mean 'is
> defined as'. It's not really a part of FOL, that I'm aware of, but it
> makes sense.
>
> Just to clarify what I was talking about above, in this situation, Joe
> and p are not propositions, though, they are a constant and a variable.

Having mulled, I would say first that of course I agree, Joe is a constant, and p is a variable, but additionally I should have stated that p was a member of the set of facts the database has been given, F. However, thanks, you are totally correct that a proposition is hardly going to have a hair colour itself and this seems rather obvious in hindsight. It may however contain a role (or attribute) called Hair_colour. So a better SOL representation would be:

Ep Role(p, Name, Joe) & Role(p, Hair_colour, Red) & p member_of F.

I think i'll stop there. I'm getting paranoid that I'm starting to look like neo with these random explorations.

> So, to relate this to the relation
>
> HasHair(Person:p, Hair:h)
>
> you have to do something more than just have an Ep around. HasHair is
> not in the domain of the Exists.
>

As a caveat, I was not completely clear exactly how to interpret this last line - I read it as indicating a proposition does not have hair, so the predicate is outside its domain, but I am not entirely confident I have understood it correctly. Received on Tue Jan 23 2007 - 19:13:48 CET