Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!lll-crg!mordor!sri-spam!nike!ucbcad!ucbvax!lasso.UUCP!ralph
From: ralph@lasso.UUCP (Ralph P. Sobek)
Newsgroups: mod.ai
Subject: Re: queries about expert systems (Vol 4, no. 187)
Message-ID: <8609231020.AA18511@inria.UUCP>
Date: Thu, 25-Sep-86 01:26:00 EDT
Article-I.D.: inria.8609231020.AA18511
Posted: Thu Sep 25 01:26:00 1986
Date-Received: Thu, 25-Sep-86 05:06:47 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 33
Approved: ailist@sri-stripe.arpa

Herb,

  >1. Production systems are the implementation of many expert systems.
  >In what other forms are "expert systems" implemented?

	I recommend the book "A Guide to Expert Systems," by Donald 
Waterman.  It describes many expert systems, which fall more or less 
into your definition, and in what they are implemented.  Production
Systems (PSs) can basically be divided into forward-chaining (R1/XCON) and 
backward-chaining (EMYCIN); mixed systems which do both exist.  Other
representations include frame-based (SRL), semantic nets (KAS), object-
oriented, and logic-based.  The representation used often depends on what
is available in the underlying Expert System Tool.  Tools now exist which
provide an intergrated package of representation structures for the expert
system builder to use, e.g., KEE and LOOPS.  Expert systems are also written
in standard procedural languages such as Lisp, C, Pascal, and even Fortran.

  >2. A production system is in essence a set of rules that state that
  >"IF X occurs, THEN take action Y."  System designers must anticipate
  >the set of "X" that can occur.  What if something happens that is not
  >anticipated in the specified set of "X"?  I assert that the most
  >common result in such cases is that nothing happens.

	In both forward-chaining and backward-chaining PSs nothing happens.
If the PS produces "X" then we can verify if "X" is never used.  In the 
general case, if "X" comes from some arbitrary source there is no
guarantee that the PS (or any other system) will even see the datum.

	Ralph P. Sobek

UUCP:	mcvax!inria!lasso!ralph@SEISMO.CSS.GOV
ARPA:	sobek@ucbernie.Berkeley.EDU	(automatic forwarding)
BITNET:	SOBEK@FRMOP11