Re: MV Keys

From: JOG <jog_at_cs.nott.ac.uk>
Date: 8 Mar 2006 12:49:39 -0800
Message-ID: <1141850979.335670.215370@u72g2000cwu.googlegroups.com>

vc wrote:
> 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.

valid FOL sentences:

age(Joe, 30)

value(x, 2)

discuss ;)

>


> >  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 - 14:49:39 CST