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From: rapaport@cse.buffalo.edu (William J. Rapaport)
Newsgroups: sunyab.cse.740
Subject: SNePS TUTORIAL QUESTION
Date: Wed, 4 Feb 2004 14:35:28 -0500 (EST)
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A student writes:

> 1) in the following expression (found at
> 
> http://www.cse.buffalo.edu/sneps/Tutorial/node70.html)
> 
> 
> (describe (assert forall $r
>                   ant (build member *r class Roman)
>                   cq  (build min 1 max 1
>                              arg ((build arg1 *r
>                                          rel loyal\ to
>                                          arg2 Caesar)
>                                   (build arg1 *r
>                                          rel hate
>                                          arg2 Caesar)))))
> 
> it looks as if there are two nodes attached to a single relation arc:
> 
> relation arc -   arg
> nodes -          (build arg1 *r rel loyal\ to arg2 Caesar) and
>                  (build arg1 *r rel hate arg2 Caesar)
> 
> I understand the semantics of the expression I just have hard time
> picturing it.

That's because it can't easily be pictured! :-)  SNePS relations, like
"arg", actually take *sets* of nodes as arguments.  So, in the above
expression, "arg" takes a set of two nodes, one representing "r is loyal
to Caesar" and the other representing "r hates Caesar".  SNePS allows
this very same situation to be described in a clearer way:

(describe (assert forall $r
                  ant (build member *r class Roman)
                  cq  (build min 1 max 1
                             arg (build arg1 *r rel loyal\ to arg2 Caesar)
			     arg (build arg1 *r rel hate arg2 Caesar))))

So:  A *single* "arg" arc pointing to a set of 2 nodes is equivalent to 2
"arg" arcs each pointing to one of those 2 nodes.
			

> 
> 
> 2) Should the expression "Elephants are animals." from programming project
> 1 be interpreted as ALL Elephants are animals (i.e. for all x if x is an
> elephant than it belongs to the class of animals) or simply elephant is a
> member of class of animals?

Your choice; just be consistent.