The Declarative Representation and Procedural Simulation of Causality in Physical Mechanisms

T h e r e i s q u i t e o f t e n a need t o s u p p r e s s much o f t h e r e p r e s e n t a t i o n o r s i m u l a t i o n d e t a i l p r e s e n t i n t h e s y s t e m s f u l l m o d e l o f a g i v e n mechan i sm. T h e r e w o u l d be a need f o r s u p p r e s s s i o n o f d e t a i l , f o r e x a m p l e , i f we. w i s h e d t o p r o v i d e a v e r y h i g h l e v e l o v e r v i e w o f a mechan ism t o s e r v e , s a y , a s a b l a c k box i n a l a r g e r i n v e n t i o n e f f o r t , o r a s a n i n t r o d u c t i o n o f t h e mechan ism t o a t o t a l l y n a i v e CAI u s e r . S i n c e t h e s u p p r e s s i o n o f mechan ism d e t a i l i s a n a l o g o u s t o t h e s u p p r e s s i o n o f d e t a i l i n t e x t , we use t h e t e r m " a b s t r a c t i o n 1 . One o f o u r c u r r e n t a r e a s o f i n t e r e s t i s i n a u t o m a t i n g t h e p r o c e s s o f mechanisms a b s t r a c t i o n . No te t h a t w e a l r e a d y have p r o v i s i o n s i n t he r e p r e s e n t a t i o n t o r e x p r e s s i n g a b s t r a c t e d f o r m s : t h e s t a t e c o u p l i n g l i n k . T h i s l i n k a l l o w s u s the f r e e d o m o f d i r e c t s t a t e s t a t e c a u s a l i t y . The a b s t r a c t i o n t e c h n i q u e can t h e r e f o r e b e one o f s y n t a c t i c a l l y r e p l a c i n g c e r t a i n p a t t e r n s i n t h e d e t a i l e d r e p r e s e n t a t i o n w i t h s t a t e c o u p l i n g l i n k s . I t a p p e a r s t h a t t h e r e w i l l b e o n l y a s m a l l number o f s y n t a c t i c a b s t r a c t i o n r u l e s . Two o f t h e most o b v i o u s a b s t r a c t i n g r u l e s a r e d e p i c t e d b e l o w . Such r u l e s , a p p l i e d t r a n s i t i v e l y , c o u l d p e r f o r m b o t h m i n o r and m a j o r a b s t r a c t i o n s . A m a j o r a b s t r a c t i o n w o u l d amount t o a s i m p l e c o u p l i n g be tween t he i n p u t and o u t p u t s t a t e s o f a mecha n i s m , e . g . " A f a l l i n g t e m p e r a t u r e causes t h e t h e r m o s t a t t o c l o s e . " Such a b s t r a c t i n g w o u l d b e a p p l i e d t o t h e d e c l a r a t i v e r e p r e s e n t a t i o n b e f o r e s i m u l a t i o n , s o t h a t t h e c o n v e r t e d c o m p u t a t i o n u n i t s w o u l d d i r e c t l y r e f l e c t t h e a b s t r a c t i o n . A b s t r a c t i o n c o u l d b e a p p l i e d u n i f o r m l y o v e r a n e n t i r e m e c h a n i s m , o r l o c a l l y t o e x c i s e p a r t s w h i c h a r e n o t o f i m m e d i a t e i n t e r e s t . N o n u n i f o r m a b s t r a c t i n g , i n w h i c h a l l u n i n t e r e s t i n g s e c t i o n s have been d e f o c u s s e d , w o u l d d e l i v e r p r a c t i c a l a d v a n t a g e s b y a l l o w i n g t he s i m u l a t o r t o d e v o t e more t i m e t o the r e l e v a n t a s p e c t s o f t h e s i m u l a t i o n . T h i s c o u l d b e i m p o r t a n t i f , f o r e x a m p l e , w e s u s p e c t t h e a u d i o s t a g e s o f a r a d i o a r e a t f a u l t , b u t know t h e power s u p p l y i s f u n c t i o n a l . B e f o r e s i m u l a t i o n , t h e r a d i o ' s power s u p p l y d e s c r i p t i o n c o u l d b e d e f o c u s s e d b e f o r e c o n v e r s i o n t o s i m u l a t i o n r e p r e s e n t a t i o n ( i . e . p o p u l a t i o n o f S C ' s ) . TWO OLFOCUSSING RULES I n a d d i t i o n t o s i m p l e s y n t a c t i c d e f o c u s s i n g , w e w i l l a l s o b e e x p l o r i n g more s e m a n t i c f o r m s . S e m a n t i c mechan i sms a b s t r a c t i o n w o u l d b e u s e f u l i f , f o r e x a m p l e , w e w i s h e d t o know a b o u t t h e gas f u r n a c e w i t h r e s p e c t t o a p a r t i c u l a r a s p e c t o f i t s o p e r a t i o n , such a s " h e a t p r o d u c t i o n 1 . W e m i g h t s c a n t h r o u g h t h e d e s c r i p t i o n , a s s e s s i n g each e v e n t a c c o r d i n g t o i t s s e m a n t i c r e l e v a n c e t o t h e c o n c e p t o f h e a t p r o d u c t i o n . T h e n , u s i n g t h e H i g h l y r a n k e d e v e n t s a s m i l e s t o n e e v e n t s , t h e s y n t a c t i c a b s t r a c t i o n p r o c e d u r e c o u l d b e a p p l i e d t o y i e l d a n a b Knowlege R e p r . 4 : R l e g e r 255Brown, J . , and Bur ton , R., M u l t i p l e Representa-t i o n s o f Knowledge f o r T u t o r i a l Reasoning, inRepresentat ion and Understanding, D. Bobrow andA. 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