How Expert Should an Expert System Be?

A computer system which a i d s computer e n g i n eers i n f a u l t d i a g n o s i s i s d e s c r i b e d . The sys tem, c a l l e d CRIB (Computer R e t r i e v a l I nc idence Bank) i s shown t o f i t i n t o the c l a s s o f p a t t e r n d i r e c t e d i n f e r e n c e sys tems. Emphasis is p laced on the " b e f o r e " and " a f t e r " phases o f system g e n e r a t i o n and i t i s shown why, to be c a l l e d an e x p e r t sys tem, these phases are i m p o r t a n t . The forms of knowledge used in CRIB a re shown to be adequate f o r d i a g n o s i s and ye t possess l i t t l e o f the s t r u c t u r a l o r f u n c t i o n a l knowledge o f more advanced e x p e r t sys tems. Summaries are g i v e n o f the t h r e e phases o f i m p l e m e n t a t i o n : e l i c i t a t i o n , imp lemen ta t i on o f knowledge s t r u c t u r e s , v a l i d a t i o n and improvement . The idea of an e x p e r t system as a "model of competence" i s ment ioned and the t r a n s f e r r a n c e o f the system a r c h i t e c t u r e t o s o f t w a r e d i a g n o s i s , us i ng the same mode l , i s d e s c r i b e d . There are s h o r t d i s cuss ions of system per formance and the n a t u r e o f e x p e r t sys tems. 1 . I n t r o d u c t i o n Th i s paper , w h i l s t a l s o be ing a v e h i c l e f o r p r e s e n t i n g the work on CRIB c a r r i e d out between 197*4 and 1979. a t t e m p t s to i n v e s t i g a t e the " b e f o r e " and " a f t e r " o f an e x p e r t sys tem. Most o f the papers w r i t t e n on and around the f i e l d o f knowledge e n g i n e e r i n g systems have c o n c e n t r a t e d on the s t r u c t u r e o f the program i t s e l f w i t h s h o r t d i s cuss ions of how the program came i n t o be ing and how the program per fo rms " i n the f i e l d " . However, an expe r t system is a non-academic e x e r c i s e (no t to say commerc ia l ) and the t w i n needs t h e r e f o r e to get the d e t a i l r i g h t beforehand and the p e r f o r m ance r i g h t a f t e r w a r d s , a re e q u a l l y i m p o r t a n t as the system d e s i g n . Four phases o f the r o u t e to a v i a b l e e x p e r t system may be d i s t i n g u i s h e d . They are no t d i s s i m i l a r t o the s t a g i n g o f the development o f any commercia l computer sys tem. They a r e : 1 . E l i c i t a t i o n f o r the f i r s t a p p r o x i m a t i o n