Ontologies and theories

John McCarthy <jmc@sail.stanford.edu>
Date: Fri, 21 Aug 92 23:50:22 -0700
From: John McCarthy <jmc@sail.stanford.edu>
Message-id: <9208220650.AA27083@SAIL.Stanford.EDU>
To: sowa@watson.ibm.com
Cc: GRUBER@sumex-aim.stanford.edu, SRKB@isi.edu, INTERLINGUA@isi.edu
In-reply-to: sowa@watson.ibm.com's message of Fri, 21 Aug 92 21:57:24 EDT <199208220202.AA08410@quark.isi.edu>
Subject: Ontologies and theories
Reply-To: jmc@cs.stanford.edu

These are purely terminological remarks.  I hope to make some substantive
remarks later.

1. F = ma was proposed as a definition of force by Ernst Mach.  I don't
think he was right to do so, but it can be done.  At present, actually
since 1987, the meter has been defined in terms of the second using
a conventional value, c = 299 792 458 m/sec exactly for the velocity
of light.  Should further advancce in science make possible comparing
two lengths more accurately than using electromagnetic radiation,
the International Bureau of Weights and Measures might go back to
a separate standard of length.  The point is that what is a definition
and what is a law is dependent on the current state of science.
KIF should also allow this flexibility.

2. The mathematicians do use logics that distinguish what computer
scientists call types.  They call them sorts and refer to multi-sorted
logics.  The word "type" is used for the positions in the hierarchy of
predicates and functions whose arguments are predicates and functions.
It is regrettable that the word "type" was taken into computer science
by people who didn't trouble to look it up.  The problem is that
computer science needs both sorts and types in the mathematical sense.
It would be good if KIF were to use the mathematicians' terminology
since it suits computer science better than what has become customary
in computer science.

3. The dictionary and philosophical usage use "ontology" to refer to
what exists.  In the old days there were arguments about the existence
of various things.  Quine made the term technical, saying that the
ontology of a theory is the correspondence between variables in the
theory and the domains in which they take their values.  Roughly
then, the ontology of a theory is given by the kinds of things assumed
to exist over which the variables can range.  This usage is also
more appropriate for computer science than the fuzziness of current
computer science usage.