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From: srt@aerospace.aero.org (Scott "TCB" Turner)
Newsgroups: comp.ai
Subject: Re: CLIPS OR NEXPERT
Message-ID: <85250@aerospace.AERO.ORG>
Date: 11 Sep 90 19:53:47 GMT
References: <1084@aviary.Stars.Reston.Unisys.COM>
Reply-To: srt@aero.UUCP (Scott "TCB" Turner)
Organization: The Aerospace Corporation, El Segundo, CA
Lines: 36

I've been using Nexpert for several years and have a number of
objections.

The documentation is opaque or missing on a number of areas that are
essential to building a large real-world application.  In particular,
the internal mechanics of the inference engine are not described at
all.  Hence it is impossible to determine how mechanisms such as
normal rule-firing and if-change actions interact.

The user interface is often cumbersome to use.  We have built much of
our knowledge base in a normal text editor (using Nexpert's lispy
internal syntax) rather than use the rule editor.  There are also some
strikingly bad design decisions, such as organizing the knowledge base
according to the name of the hypothesis rather than the name of the
rule.

Debugging can be painful.  If the inference engine enters a loop it 
will often not respond to user commands, forcing an interrupt and 
restart.  Many of the error messages are nearly useless.  If a loop
is detected during backward chaining, the user gets a message to that
effect - but no indication as to what rule caused the message!

Overall, Nexpert strikes me as having been designed by the marketing
department and never tested on real problems.  (I know, it is the best
selling tool.  What can I say?  I'm merely reporting my experiences.)
Don't be too impressed by the spiffy features such as the graphic
display of the inference tree.  That's the kind of thing that looks
great during a demo and is rarely used during development.

I do not recommend Nexpert.  Our own group is looking for a different
tool for our future projects.

					-- Scott Turner

This posting reflects my opinions, and not those of The Aerospace
Corporation.