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From: wdavis@x102c.harris-atd.com (davis william 26373)
Newsgroups: comp.ai
Subject: Re: Verification of KB Systems
Message-ID: <5195@trantor.harris-atd.com>
Date: 7 Jan 91 14:21:21 GMT
References: <1991Jan4.180056.20917@evax.arl.utexas.edu>
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Reply-To: wdavis@x102c.ess.harris.com (davis william 26373)
Organization: Harris Corporation GSS, Melbourne, Florida
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In article <1991Jan4.180056.20917@evax.arl.utexas.edu> mullen@evax.arl.utexas.edu (Dan Mullen) writes:
>In the proceedings from WESTEX-87 Green and Keyer say that nobody does
>V&V of expert systems because nobody knows how to do it. And nobody knows
>how to do it because nobody ever asks for it to be done.  ...
 (some lines deleted)
>... Or would anyone like to offer a proof that verification
>of KB systems is impossible?

This is not exactly a proof, but think about what you are asking for
and it seems impossible.  For a non-expert system, you can specify
requirements rigorously.  They may not be the correct requirements,
but they can be clear.  A system claiming to implement those requirements
can be validated, to some extent, against those requirements.
Maybe something useful is produced in the process, maybe not.
Usually new requirements are discovered during or after implementation
(I have not seen a project yet that did not involve some derived
requirements during the project or a market driven change).

How would we specify the precise requirements for an expert system?
Start with the fuzzy "It should be an expert" or "It should be
as expert as possible within the budget and time constraints" or
even "It should know what these experts know".  Now take two experts
and put them in a room and see if they agree on everything in their
area of expertise.  If not, then which knowledge is correct for
the expert system?

It may be possible to check all the rules against experts to see
if they agree and it may be possible to check the inference
engine with validation techniques, but is this sufficient to
validate an expert system?  What about knowledge that is learned
as the system evolves?

I don't know how to completely validate a person's knowledge of
a subject.  So, I don't feel confident that a computer's knowledge
of a subject can be any better validated.  Even more problematic
is that the computer may have missing knowledge - how is that to
be validated (that none is missing)?