Re: MV Keys

Brian Selzer wrote:
> "vc" <boston103_at_hotmail.com> wrote in message
> news:1141824160.347616.85480_at_i40g2000cwc.googlegroups.com...
> >
> > Brian Selzer wrote:
> > [...]
> >> "x is 2" is a sentence; "y is 3" is a sentence.
> >> "x is 2 and y is 3" is also a sentence.
> >
> > You are confused. "x is 2" is not a sentence in the contex of FOL.
> > It's a predicate with a free variable which will become a sentence if
> > you substitute a constant for x.
> >
>
> It isn't? So, what you're saying is the statement, "Joe is 30 years old" is
> not a statement in FOL?

"Joe is 30 years old" is a FOL sentence allright.

> As I said, I'm not a logician, so I don't speak
> their jargon. I guess I don't speak their language either.
>
> If E(x in X)(x = 2) and E(y in Y)(y = 3) are predicates, would a predicate
> with an variable that belongs to the cartesian coordinate domain be a
> statement in second order logic?

No, the difference is that in FOL, a variable can range over individuals, while in SOL it can do so over predicates/properties as well (a predicate can be a variable).
.

>
> >
> >>Thus a tuple in a relation R{A, B, C} is the
> >> set of propositions {A has value 3, B has value 7, C has value 2}. 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.
> >
> > You are confused even more. A relation is simply an interpretation of
> > some predicate (which is an element of a FOL language). A tuple is an
> > element of such relation.
> >
> So, you're saying that an element of a relation doesn't have a truth value?

An element of a relation is just that -- an element of a certain set. Received on Wed Mar 08 2006 - 20:59:30 CET