[SCL] new draft

[John F. Sowa]

Frank,

Your note raised several issues, and I'll respond
briefly to each of them.

Re CL & SCL lists:  The original list was named KIF,
and it was renamed CL for Common Logic.  Earlier
this year, a less ambitious version of CL, called
Simplified Common Logic or SCL, was set up in order
to get more rapid agreement on basic issues.  Since
then, the SCL list has been devoted to rather detailed
technical discussions, and CL will be used for progress
reports about settled issues and for drafts that are
progressing toward the standard.  Essentially all of
the SCL participants are also subscribed to CL, but
CL will be devoted more to standards related issues
than to technical issues in logic.

Re Z:  The relationship between Z and CL was discussed
at the SC32 WG2 meeting in Santa Fe in January.  The
slides, which were prepared by Pat Hayes, Chris Menzel,
and me and which I presented to WG2, discuss these issues:

   http://www.jfsowa.com/talks/clprop.htm

In short, Z and CL do have a large overlap, but they were
designed for different purposes:

  1. CL is designed to serve as a common semantic base
     for multiple logic-based languages, each of which
     has been designed for a different purpose, but each
     of which has a large overlap with the others.

  2. Z was designed as a specification language, not as
     a target language for translations to and from other
     logic-based languages.

For these reasons, CL supports a broader range of semantics
than Z.  Every feature of Z can be translated to CL
(or SCL core).  But it is not possible to translate all
of CL (or even SCL core) to Z.

One of the major reasons why Z cannot be used as a target
for translations to and from other versions of logic is
that it has a very strict typing system.  But many of
the languages that we need to support with CL are either
untyped, have optional types, or have less rigorously
enforced type constraints than Z.

Therefore, the SCL core is untyped, but it can support
a wide variety of typing systems, including the strict
typing of Z, the optional types of conceptual graphs,
and untyped versions of RDF and OWL.  It is possible to
translate Z to SCL, but it is not possible to translate
SCL, CL, and many other logic-based languages to Z.

For the proposed CL standard, we plan to include an
annex that shows how Z can be translated to CL.  That
translation would make Z a CL-conformant language.

Re definitions of terms:  There will be a glossary of
all technical terms in the draft CL stsandard for May '04.

If you have tuned in to some of the ongoing discussions,
you may have noticed that we are still arguing over some
of the terminology.  We have actually reached a greater
consensus on the technical issues than on the terms we
should use to describe them.

The reason for the disagreements is that we are
addressing a multidisciplinary audience of logicians,
computer scientists, and software developers.  Over
time, these groups have adopted different words for
very similar concepts.  We therefore have an abundance
of terminology, and we are trying to decide which
are the most common and most readily understood terms
(which are sometimes quite different from the highly
specialized terminology used by the logicians).

John Sowa