Re: Issue with top-down and bottom-up semantics

Hi Francis,

I agree with your objection to the "flat model for variable
quantification".  In fact,
the semantics we use is not flat.  In our query language if a variable
appears in two
disjuncts, but not "outside" of them, it is considered to be two different
variables,
independently quantified. If you flatten, you get a semantics that most
users would
find non-intuitive.

We consider much of  NaF semantics to be a property of individual operators,
rather than
of the language itself (or the model).  Thus, for example, if a user wants
to use UNSAID, she
can, and which uses negation as failure, and if she wants to use NOT
(classical negation) she
can use that.  We don't happen to support two different OPTIONAL operators,
but we could if
there were a need for that.

I'm not objecting to open world semantics per se; there are (a minority of)
cases when its
useful.  I'm objecting to the absence of closed world semantics.

Cheers, Bob