Framed Painting

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A F r a m e d P A I N T I N G :

T h e R e p r e s e n t a t i o n o f a C o m m o n

K n o w l e d g e F r a g m e n t

E U G E N E C H A R N I A K

University of eneva

S e ns e

This paper presents a fr am e representation for comm on sense knowledge and uses it

to formalize our knowledge of m un dan e painting (walls, not portraits). These frames,

while designed to aid a comp uter program to understand stories about the painting process,

should be of use to program s which attempt to actually carry out the activity. The paper

stresses a d ee p understanding of the activity so that the representation indicates not Only

what steps to carry out, but also how to do them, and why they should be done. To

accomplish this, while at the same time preserving modularity and nonredundancy, a

system of interframe pointers is in troduced (the COM ES-FROM and LE AD S-TO point-

ers) wh ich explain how or w hy something is done in terms of know ledge given in other

frames. The paper proc eeds by steadily deepening an initial English-like description of the

activity, and a context free grammar for the representation is included.

T h e r e i s a c o m m o n a g r e e m e n t a m o n g A r t i f i c i a l I n t e l l i g e n c e r e s e a r c h e r s th a t

i n t e l li g e n t b e h a v i o r r e q u ir e s l a r g e b o d i e s o f d o m a i n - s p e c i f i c k n o w l e d g e , b e i t

c h e s s , m e d i c i n e , o r t h e g e n e r a l c o m m o n s e n s e k n o w l e d g e w h i c h a ll m e m b e r s

o f o u r c u l tu r e s h a r e . N a t u r a l l y , s u c h a g r e e m e n t h a s l e d t o a r a p i d l y g r o w i n g

l i te r a t u re a b o u t h o w s u c h k n o w l e d g e c o u l d b e r e p r e s e n t e d a n d o r g a n i z e d . T h e

p r e s e n t p a p e r i s a n a d d i t i o n t o t h i s l i t e r a t u r e .

I n p a r t i c u l a r I w i l l d e v e l o p h e r e a f o r m a l i z a t i o n o f o u r k n o w l e d g e c o n c e r n i n g

w h a t m i g h t b e c a l le d m u n d a n e p a i n ti n g . T h a t is , w e w i l l b e c o n c e r n e d w i th

o u r k n o w l e d g e o f h o w o n e g o e s a b o u t p a i n t i n g o b j e c ts l i k e w a l ls a n d b o o k c a s e s ,

a s o p p o s e d to t h e a r t i s t i c p a i n t i n g o f s t i ll l i v e s a n d p o r t r a i t s . I a m c u r r e n t l y

d e s i g n i n g a p r o g r a m w h i c h w i l l u se t h i s k n o w l e d g e b a s e t o u n d e r s t a n d s i m p l e

s t o ri e s a b o u t p a i n t i n g a n d d e m o n s t r a t e i ts u n d e r s t a n d i n g b y i t s a b il i t y t o a n s w e r

q u e s t i o n s a b o u t t h e s t o r i e s ( s e e C h a r n i a k , 1 9 7 7 ). B u t w h i l e I s h a l l b e p r i m a r i l y

c o n c e r n e d w i t h th e u s e o f s u c h k n o w l e d g e i n l a n g u a g e c o m p r e h e n s i o n , t h e

f o rf ia a li sm d e v e l o p e d h e r e s h o u l d b e e q u a l l y r e l e v a n t t o th e c o n s t r u c t i o n o f

p r o g r a m s w h i c h a r e a b l e , i n a n i n t e l l i g e n t f a s h i o n , t o a c t u a l l y p a i n t . T h a t t h e

r e p r e s e n t a t io n h a v e t h i s p r o p e r t y i s o n e o f t h e c o n s tr a i n t s I h a v e a d o p t e d , o n t h e

g r o u n d s t h at a s p e c i a l a n d d i s t i n c t k n o w l e d g e b a s e , u s e d s o l e l y f o r l a n g u a g e

*Reprints of this article may be obtained from P rofessor Eugene Cham iak, Yale University, De-

partment of Computer Science, 10 Hillhouse Avenue, New Haven, Conn. 06520.

355


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356 EUGENE CHARNIAK

c om pr e he n s ion , s e e m s qu i t e imp la us ib l e , a t l ea s t f o r a c t iv i t i e s l i ke pa in t ing . Th i s

too i s a c om m on v i e w in Ar t i f ic i a l I n t e l li ge nc e c i r c l e s , bu t l i tt l e i f a ny th in g in t he

p r e se n t pa pe r de pe nd s on i t . I n pa r ti c u l a r , wh i l e upon som e oc c a s ion s I w i l l

i n t r oduc e a ne w f a c t i n to the r e p r e se n ta t ion be c a use i t i s c l e a r t ha t a r e a l pa in t e r

wou ld ne e d suc h a f a c t , i n a ll c a se s a n a pp r op r i a t e s to r y c ou ld be c o ns t r uc t e d to

de m ons t r a t e the s a me ne e d in the dom a in o f que s t ion a nsw e r ing . I nde e d , f o r t he

l e s s i n tu i t i ve c a se s I w i l l p r ov ide suc h s to r y e xa mple s .

T h e c o n s e n s u s m e n t i o n e d i n t h e o p e n i n g p a r a g r a p h a l l o w s o n e t o s a f e l y s k ip

ov e r the o the r w i se o b l iga to r y ju s t i f i c a t ion f o r t he l i ne o f r e se a r c h in que s t ion ,,B u t

in do ing so , i t s imu l t a ne ous ly p r e se n t s a d i f f e r e n t a nd , i f a ny th ing , m or e d i f f i c u l t

t a s k - - t h a t o f d is t in g u i sh i n g o n e s r e s e ar c h f r o m t h e m a n y p a p e r s o n c l e a r ly

r e l a te d top i c s . T o th i s e nd l e t me n o te tha t t he r e p r e se n ta t ion p r e se n te d h e r e ha s ,

a t it s h e a r t , t h e p r o b l e m o f d e p t h o f u n d e r s t a n d i n g a n d t h e c o n c u r r e n t c o m p l e x i t y

o f k n o w l e d g e w h i c h r e a s o n a b l y d e e p u n d e r s t an d i n g i n v o l v e s . S o , i n th e d o m a i n

o f pa in t ing , w he n I spe a k o f de p th o f unde r s t a nd ing , I me a n tha t it is no t

su f f i ci e n t f o r a p r og r a m to k now tha t one sho u ld wa sh a pa in t b r ush a f t e r

p a i n t i n g - - o n e s h o u ld a l s o k n o w h o w t o d o i t, w h a t w i l l h a p p e n i f i t i s n o t d o n e ,

a nd w hy the pa in t e r s i n t e n t ion to t h r ow the b rush a wa y a f t e r u s ing i t c ons t i t u t e s

a re a son wh y the o the r w i se u se f u l sugge s t ion c a n be igno r e d in t h is c a se . S imi -

l a rl y , i f w e w i s h e d t o f o r m a l i z e o u r k n o w l e d g e o f h o w t o s e n d a l e t te r , w e s h o u l d

ind ic a te no t on ly t hat a s t a mp shou ld be a f f ixe d , bu t a ga in , how , w hy , a nd w ha t

ma y ha ppe n i f i t i s no t done .

T o s e e h o w s u c h d e e p u n d e r s ta n d i n g i n v o l v e s u s in p r o b l e m s o f c o m p l e x i t y o f

r e l a te d know le dge , l e t u s c ons ide r t he s ta mp e xa m ple i n a b it mor e de t a i l . A f i r s t

g u e s s a t h o w w e m i g h t o r g a n i z e o u r k n o w l e d g e o f l e t t e r m a i l i n g w o u l d b e t o

wr i t e dow n a s e r i e s o f i n s t r uc tions wh ic h e xp la in e xa c t ly wha t o ne do e s i n o r de r

to a c c ompl i sh the t a sk . Th i s i s e spe c i a l l y r e a sona b le g ive n the e a r l i e r c omme n t

a bou t wa n t ing the r e p r e se n ta t ion to be a pp l i c a b le , no t on ly t o s to r y c ompr e he n -

s ion , bu t t o a c tua l ly pe r f o r m ing the a c t iv i ty . B u t as soon a s we de c ide to o r ga n iz e

ou r l e t t e r ma i l i ng f r a m e in th i s f a sh ion we a r e imm e d ia t e ly c o n f r on te d by the f a c t

tha t t he re a sons f o r do ing m a ny o f t he a c tiv i t ie s t he r e in ha v e no th ing to do w i th

the a c t ions one i s pe r f o r m ing , a nd e ve r y th in g to do w i th t he a c t ions one e x pe c t s

the pos t o f f i c e t o pe r f o r m . I nde e d , ha v ing o nc e de c id e d on a l e t t e r ma i l i ng f r a m e ,

o n e i m m e d i a t e l y n e e d s a p o s t o f f i c e f r a m e , a n d c o m p l e x i n t e r c o n n e c t i o n s b e -

twe e n the two ; some th ing wh ic h migh t l ook l i ke F ig . 1 .

O n e m i g h t , o f c o u r s e , s i m p l y d i s p e n se w i t h t w o s e p a ra t e f r a m e s , a n d c o m b i n e

the two in to one , bu t t he r e a r e s e ve r a l r e a sons a ga ins t suc h a ma n e uve r . F o r on e

th ing i t wou ld be c ome mor e d i f f i c u l t t o s e e ou r f r a me s a s t e l l i ng u s how to

pe r f o r m the a c tiv i ti e s i n que s t ion , s inc e the y w ou ld n ow inc lude m a ny a c t ions t o

b e p e r f o r m e d b y o t h e r s. F u r t h e r m o r e , o n e r e a s o n f o r s p li tt in g u p o u r k n o w l e d g e

in the f ir s t p l a c e is t o he lp be a t t he c om bina to r i a l e xp los ion . Th a t i s , we wa n t t o

k e e p d o w n t h e a m o u n t o f i n f o r m a t i o n w e n e e d a t an y p o i n t o f a s t o r y , o r a t a n y

po in t i n ou r r e a l l i f e a c t iv i t i e s , s i nc e f a i l u r e t o do so me a ns r a p id ly g r owing


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A F R A M E D P A I N T I N G

357

F I G I T h e r e l a ti o n o f l e t te r m a i l i n g t o t h e P o s t

p r o b l e m s o f s e a r c h i n g o u r k n o w l e d g e b a s e f o r t h o s e f a c t s w h i c h a r e i n d e e d

re l evan t to t he s i t ua t ion a t hand . F ina l l y , a l t hough t h i s is no t so obv iou s i n t he

above exam ple , i n m any cases ( i nc lud ing t hose we w i ll enc oun t e r i n pa in t i ng ) to

e f f e c t

su h

a c o m b i n a t i o n r e q u i r e s r e p e a t i n g p i e c e s o f k n o w l e d g e m a n y t i m e s

o v e r b e c a u s e t h e y c o m e i n to p l a y in m a n y s i t u a ti o n s . G i v e n t he e n o r m o u s n u m -

ber s o f f ac t s peop l e s eem to use , t o mu l t i p ly ou r s t o rage p rob l em by 50 o r 100 by

such p ro f l i gacy s eems i nadv i sab l e a t bes t .

I f we t u rn now to pa in t i ng we no t e t ha t i t i s no rmal ly pe r fo rmed by a s i ng l e

p e r so n . H e n c e w e d o n o t h a v e e x a c t l y t h e k i n d o f i n te r d e p e n d e n c e b e t w e e n l e tt e r

m a i l i n g a n d p o st o f f ic e s . B u t w e d o h a v e s o m e t h i n g s im i l a r in t h e d e p e n d e n c e o f

p a i n ti n g o n t h e c o m m o n s e n s e p h y s i c s a n d c h e m i s tr y t h a t u n d e r l ie i t. F o r e x a m -

p l e , i f o n e i s t o u n d e r s ta n d w h y w e w a s h a p a in t b r u sh w e m u s t u n d e r s t a n d th e

genera l p roper t ie s o f evapo ra t i on , t he spec i f i c p roper t i e s o f evap ora t ed pa in t , and

the advan t ages o f hav ing a pa in t b rush t ha t i s bo th f l ex ib l e and abso rban t .

W a s h i n g in tu r n r e q u ir e s k n o w l e d g e o f m i x i n g l i q u i d s , t h e n a t u re o f

h o m o g e n e i t y , a n d h o w l iq u i d s ti c k s to s u r f a c e s . I t w o u l d b e r e d u n d a n t t o i n c l u d e

a ll t h is i n f o rm a t i o n d i r e c tl y i n P A I N T I N G , s o w e a r e a g a i n f a c e d w i t h th e

p r o b l em o f r e l a ti n g t h e c o m p l e x e v e n t , P A I N T I N G , t o o t h e r e v e n t s o n w h i c h it

depends .

Req u i r i ng t ha t t he r ep resen t a ti on be capab l e o f exp res s ing such com plex i n te r -

r e l a t ed knowledge has l ed me t o i l l u s t r a t e t he r ep resen t a t i on by t he cons t an t

appea l t o one t op i c , nam ely , m und ane pa in t ing . I t i s on ly in t h i s w ay t ha t I can

bu i l d the needed k now ledge o f pa in t i ng and i ts r e la t ed t op i cs , wh ich t o ge the r wi l l

be r e fe r red t o a s t he pa in t i ng complex ( s ee F ig . 2 ) . In t ak ing t h i s app roach , o f

course , I r i sk t he pos s ib i l i t y t ha t t he r ep resen t a t i on p resen t ed wi l l no t ex t end

e a s i ly t o o t h e r d o m a i n s . B u t t o d o o t h e r w i s e , a n d c o v e r a w i d e v a r i e ty o f s u b j e c ts

wou ld e f fec t i ve ly ba r t he dep th I s eek .


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358 EUGENE CHARNIAK

roller ainting

I / ~ . ~ ~ - ~ ' ~ \ ~ / ~'~

/ / I~ absorption / re s id . . . . . l i d i f i c a t ion \ / / ~

I / fa:l p . . . . . . d I I ~ co~ino

~ / vol ume) inc teasel / ~ residue Lc on ta c/ /t I ~

: J S '.....

I \

halt fluid-containment I stuff-color

homogeneous

sticky-on stick separate contact part-of change support exterior surface

FIG. 2 The better developed frames in the painting com plex. The uncon nected frames at the

bottom play a role in so ma ny frames as to prohibit linking them to the fram es in w hich they appear.

F o r t h e m o s t p a r t , t h e r e st o f th i s p a p e r d e s c r i b e s i n s t e a d i l y m o u n t i n g d e t a i l

t h e p a i n t i n g c o m p l e x a n d t h e r e p r e s e n t a t i o n i n w h i c h i t i s w r i t te n . T h e e x c e p t i o n

is S e c t i o n 3 , t h e c o n c l u s i o n , w h i c h is a f a i r ly g e n e r a l d i s c u s s i o n o f f u t u r e w o r k

a n d th e n a t u re o f s e m a n t i c r e p r e s e n t a t i o n . S e c t i o n 1 g i v e s t h e b r o a d o u t l in e s o f

th e r e p r es e n t at io n , a n d in p a r t ic u l a r i n t ro d u c e s th e C O M E S - F R O M a n d

L E A D S - T O p o i n t e r s w h i c h a r e u s e d t o e f f e c t l i n k a g e s l i k e t h o s e w e s a w i n t h e

l e tt e r e x a m p l e . S e c t i o n 2 w il l d e s c r i b e t h e r e p r e s e n t a t i o n a ll o v e r a g a i n , b u t n o w

w e w i ll b e m u c h m o r e c o n c e r n e d w i t h t h e d e t a il s l i ke th e r e p r e s e n t a ti o n o f

c o n t i n u o u s a c t i o n s , a n d w h a t s o r t s o f v a r i a b le s w e n e e d i n o u r f ra m e s . A s t il l

g r e a t e r le v e l o f d e t a il , t h e e n t ir e p a i n t i n g c o m p l e x ( s e e F i g . 2 ) e x p r e s s e d i n f u l l

f o r m a l i s m a n d f r e e ly c o m m e n t e d , h a s b e e n o m i t te d f r o m t h e p a p e r f o r r e a s o n s o f

s p a c e . I t i s o b t a i n a b l e i n a n a p p e n d i x t o a s l ig h t l y l o n g e r v e r s i o n o f t h is p a p e r

( f r o m th e I n s ti tu t e f o r S e m a n t i c a n d C o g n i t i v e S t u d i e s ) o r s e p a r a t e l y f r o m t h e

a u t h o r .

I . T H E F U N D A M E N T A L S O F T H E R E P R E S E N T A T I O N

1 1 F r a m e s i n G e n e r a l and P a i n t i ng i n P ar t i c u l a r

T h e re a d e r m a y h a v e n o t e d t h at a l t h o u g h I h a v e u s e d t he w o r d f r a m e t w o o r

t h re e t im e s , I h a v e y e t t o d e f i n e it . I n f a c t , I h a v e b e e n t r a d i n g o n t h e c u r r e n t

p o p u l a r i t y o f th e te r m a n d a s s u m i n g t h a t th e r e a d e r w i l l h a v e a g e n e r a l i d e a o f

w h a t is m e a n t b y i t. B u t f o r t h e s a k e o f c o m p l e t e n e s s , l et m e t r y t o g i v e a

m i n i m a l d e f i n i ti o n in t h e s e n s e o f o n e w h i c h w i l l in c l u d e a ll c u r r e n t u s e s , b u t

w h i c h i s n o d o u b t i n s u f f i c i e n t t o d i s c r i m i n a t e s o m e n o n f r a m e s f r o m f r a m e s .


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A FRAMED PAINTING 359

I t a ke a f r a m e t o b e a l a r g e b o d y

o f i n f o rm a t i o n

e x p r e s s e d i n a c o m p u t e r u s a b l e

f o r m a l i s m

a bou t a s ing l e t op i c

whe r e t he f a c t s a r e r i c h ly

i n t e r c o n n e c t e d

a n d w h i c h , w h i l e t y p i c a ll y c o n s u l t e d

a s a who le

c ons i s t s o f ba si c un i ts ( f a c t s ) wh ic h a r e

ind iv idua l ly u se f u l

( a s o p p o s e d t o a s i n g l e p r e d i c a t e

c a l c u lus s t a t e me n t )

( a nd in pa r t i c u l a r no t i n na tu r a l

l a n g u a g e )

( a s o p p o s e d t o a f o r m a l i z e d

e n c y c l o p e d i a )

( u n l i k e a c o m p u t e r l i s t i n g o f s t o c k

m a r k e t p r i c e s )

( a s oppose d to t he u sua l so r t o f

se ma n t i c ne t )

( a s oppose d to a s ing l e s t a t e me n t i n a

m a t r i x m u l t i p li c a t io n r o u t i n e ).

I o r g ina l ly s t a t e d tha t I e xpe c t e d my pa in t ing f r a me to be u se f u l no t on ly i n

u n d e r s t a n d in g s t o ri e s , b u t a l so t o c o n t a i n i n f o r m a t i o n t h a t w o u l d b e u s e d t o g u i d e

the ac tua l a c t o f pa in t ing . T o sa t i s f y t h i s s e c o nd c r i t e r ion r e qu i r e s , a t t he ve r y

l e a st , t ha t t he fr a m e spe c i f y wh a t t h ings ne e d to be don e , a nd in wha t s e que nc e .

T h a t i s , o u r p a in t i n g f r a m e m i g h t l o o k s o m e t h i n g l i k e F i g . 3 .

I n F i g . 3 , I h a v e a d o p t e d a c o n v e n t i o n , w h i c h w i l l b e u s e d t h r o u g h o u t t h i s

p a p e r , o f c a p i ta l i z in g t h o s e p o r t i o n s o f t h e f r a m e w h i c h a r e i d e n ti c a l ( o r n e a rl y

so ) to the f ina l ve r s ion me n t ione d e a r l i e r . T h i s i s w hy , f o r e xa m ple , t he s ta t e -

m e n t n a m e s , P A I N T 1 , e t c . , d o n o t h a v e c o n t i g u o u s n u m b e r s . ( It a l so g i v e s

s o m e i d e a o f h o w m u c h is l e ft o u t o f t h is f i rs t tr y . )

Th e po r t i ons i n l owe r c a se a r e s imp ly Eng l i sh ph r a se s t o s t a nd in f o r the

f o rm a l i s m w h i c h , b y t h e e n d o f th e p ap e r , w i ll re p l a ce th e m . T h e s y m b o l G O A L

m a r k s t h e t y p i c a l g o a l st a te o f t h e e v e n t b e i n g d e s c r i b e d , w h i l e E V E N T m a r k s a

m o r e d e t a i l e d d e s c r i p t i o n o f t h e a c t i v i t y i t s e l f . T h e a r r o w s , o f c o u r s e , s i m p l y

ind ic a te t he t ime o r de r ing o f t he va r ious s t e ps . La s t ly , no t e t ha t I ha v e ma de the

f r a m e n e u t ra l b e t w e e n u s i n g a b r u s h o r r o l l e r b y m e n t i o n i n g n e i t h e r a n d i n s t e a d

u s i ng t h e t e rm p a i n t i n g i n s t r u m e n t . O t h e r w i s e I w o u l d t h in k t h a t t h e e x a m p l e

s h o u l d b e r e a s o n a b l y s e l f - e x p l a n a t o r y .

PAINT ING try number 1

GOAL : PAINTING-GOAL

EVENT: FPAINTINGI4

~PAINTINGI6

LPAI NTING37

FIG. 3

(object to be p ainted has a coat of paint on it)

(object is not dirty)

(LOOP

PA INT ING I7 (get paint on the painting instrument)

PAIN TING 22 (bring instrum ent in contact with object)

)

(all p aint rem oved from painting instrument)

PAINT ING try num ber I.


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360

EU G EN E CH RN I K •

A c t u a l ly t o u s e s u c h a k n o w l e d g e r e p r e s e n t a ti o n t o p a i n t w o u l d b e n o e a s y

m a t te r. I n s o m e s e n s e w e w o u l d w a n t to c o n si d e r P A I N T I N G a p i' o g ra m a nd

t hen p r oc e e d t o e x e c u t e i t. Bu t p r e c i s e l y how t h is w ou l d be done is no t c l e a r .

I n t he p r e se n t c a se t hi s i s c o m p l i c a t e d b y th e o b v i o u s s k e t c h i n e s s o f P A I N T I N G

t ry I , b u t e v e n w e r e w e in p o s s e ss i o n o f a c o m p l e t e P A I N T I N G t h e r e w o u l d s ti ll

be m uc h ne c e s s a r y i n f o r m a t i on l e f t ou t . I n pa r t i c u l a r , t o a c t ua l l y pa i n t w ou l d

r e q u ir e b a si c k n o w l e d g e a b o u t v i s io n , o r h o w t o m o v e o n e ' s a r m s a n d l e g s , a n d

c l e ar l y n e i th e r o f t h o s e t o p ic s w o u l d b e re p r e s e n te d i n P A I N T I N G . B e f o r e w e

c a n m a k e m u c h s e n se o f t he n o ti on o f e x e c u t i n g P A I N T I N G , th e r e la ti o n

b e t w e e n t h is l ev e l o f k n o w l e d g e a n d t h o se m o r e b a s i c l e v e ls u n d e r n e a th m u s t b e

e xp l i c a t e d . H o w e ve r , t h is i s no t a s k to be t a ke n up a s a si de i s s ue , a s it w o u l d be

here .

T h e i n f o r m a t i o n e x p r e s s e d i n P A I N T I N G , h o w e v e r , i s a l s o r e q u i r e d f o r

a ns w e r i ng que s t i ons a bou t s t o r i e s c onc e r n i ng pa i n t i ng . F o r e xa m pl e :

J a c k w a s go i ng t o pa i n t a c ha i r . H e w a s he d t he c ha i r .

( Q ue s t i on : W hy ? A ns w e r : O ne s hou l d no t pa i n t a d i r t y ob j e c t . Q : W h y

not? A: I t can l ead to f l ak ing . )

T he n he w i pe d t he ha nd l e o f h i s pa i n t b r u s h .

( Q : W h y ? A : I d o n ' t k n o w . )

A l i t t l e b i t l a t e r J ack d ipped the brush in the pa in t .

( Q : H a s he fi n i she d ye t ? A : N o . )

T he n he d r e w t he b r u s h a c r o s s t he c ha i r .

( Q : Cou l d t h is st e p be le f t ou t ? A : N o . Q : W hy no t ? A : Be c a us e i t i s t h i s

s t e p w h i c h ge t s t he pa i n t on t he c ha i r . )

S om e t i m e l a t e r he s t a r t e d t o c l e a n t he b r u s h .

( Q : Cou l d t h is s te p be l ef t ou t ? A : Y e s . Q : T h e n w h y i s he do i ng i t? A :

T o p r e ve n t the pa i n t f r om d r y i ng on t he b r u s h . Q : I s t ha t ba d? A : Y e s

b e c a u s e i t c a n m a k e t h e b r u s h u n a b s o r b a n t a n d i n f l e x i b l e w h i c h w o u l d

m a ke i t u s e l e s s f o r pa i n t i ng . )

I w i ll u s e s om e ne w s pa pe r t hough t J ac k:.

( Q : F o r w ha t ? A : P r oba b l y i n o r de r t o w i pe t he b r u s h on i t . )

B e s i d e s s h o w i n g h o w s u c h k n o w l e d g e c a n c o m e i n to p l a y in s to r y c o m p r e h e n -

s i on , t h i s e xa m pl e a l s o i ll u s tr a t e s the l e ve l o f unde r s t a nd i ng w h i c h t he r e p r e s e n -

t a ti on de ve l ope d he r e s hou l d be c a pa b l e o f e xh i b i t i ng . A s l it e r a t u r e , s uc h e xa m -

p l e s a r e obv i ous l y qu i t e un r e a l i s t i c , bu t i t s e e m s c l e a r t ha t i f w e c a nno t ge t a

p r o g r a m t o u n d e r s ta n d s u c h e x a m p l e s , w e w i l l h a v e l it tl e h o p e f o r m o r e c o m p l i -

ca ted (and rea l i s t i c ) ones .

T o u s e P A I N T I N G t o u n d e rs ta n d s to r ie s a b o ut p a in t in g , w h i l e b y n o m e a n s

t r i v i a l , a t l e a s t s e e m s m uc h m or e t r a c t a b l e t ha n u s i ng i t t o pa i n t . W e w i l l no t


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A FRAM ED PAINTING 361

d i s c u s s t he d e t a il s h e r e ( p r i m a r i l y b e c a u s e t h e y h a v e n o t b e e n w o r k e d o u t ) b u t t h e

b a s i c i d e a i s q u i t e s i m p l e . ( T h e r e a d e r m i g h t c o n s u l t C h a r n i a k ( 1 9 7 6 ) f o r a

l o n g e r e x p o s i t i o n o f t h e f o l l o w i n g i d e a s . F o r t h a t m a t t e r h e c o u l d a l s o c o n s u l t

S c h a n k e t a l. ( 1 9 7 5 ) o r R i e g e r ( 1 9 7 5 ) w h e r e m u c h t h e s a m e i d e a s a p p e a r . )

E s s e n t i a l l y t he i npu t s e n t e nc e i s s e e n a s i n s t a n t i a t i ng one o r m or e l i ne s o f one o r

m o r e f r a m e s . T h a t is , w h e n w e s e e Jack washed the chair in o u r e a r li e r e x a m p l e

t h e p r o g r a m i s t o u n d e r s t a n d t h i s a s i n s t a n t i a t i n g P A I N T I N G I 4 ( o b j e c t n o t

d i r t y ) . I t i s t he r o l e o f t he pa r s i ng a l go r i t hm t o t r a ns l a t e t he s e n t e nc e i n t o a f o r m

w h i c h c a n l a t e r b e u s e d t o m a k e s u c h i d e n t i f i c a t i o n b e t w e e n w h a t w e a r e t o l d i n

t h e s t o r y a n d w h a t w e h a v e s t o r e d i n o u r f r a m e s . O n c e t h i s i d e n t i f i c a t i o n i s

m a d e , t h e n i n f e r e n c e s , s u c h a s h o w f a r a lo n g J a c k i s in t he a c t o f p a i n t i n g , o r

w h y h e d i d s o m e t h i n g , a r e t o b e m a d e b y r e f e r e n c i n g t h e f r a m e . O b v i o u s l y , i f

washing the object

a p p e a r s a s it d o e s a t t h e b e g i n n i n g o f t h e e v e n t t i m e s e q u e n c e ,

t h e n J a c k c a n n o t h a v e f i n i s h e d h i s a c t i v i t y .

T o f l e s h t h i s o u t , w e m u s t s p e c i f y h o w p a r s i n g w o r k s , h o w w e s e l e c t a p p r o -

p r ia t e f r a m e s , a n d h o w w e g o a b o u t l o o k i n g f o r m a t c h i n g s t a te m e n t s w i t h in t h o s e

f r a m e s . Bu t a s I s a i d , t he s e i s s ue s w i l l no t be de a l t w i t h he r e .

1.2 Methods and COMES FROM

W e n o t e d e a r l i e r th a t o u r f ir s t tr y a t a p a i n ti n g f r a m e c o n t a i n e d n o t h i n g l i k e th e

n e c e s s a r y b r e a d t h o f i n f o r m a t i o n . B u t e q u a l l y i m p o r t a n t , n e i t h e r d o e s it c o n t a i n

t he ne c e s s a r y de p t h . T ha t i s , t o r e pe a t m y e a r l i e r e xa m pl e , i t s t a t e s t ha t t he

i n s t r u m e n t u s e d i n t h e p a i n t i n g s h o u l d b e c l e a n e d , b u t n o t h o w a n d w h y . T h i s

f ir s t p o r t i o n o f t h e p a p e r w i ll b e p r i m a r i l y c o n c e r n e d w i t h h o w s u c h i n f o r m a t i o n

i s t o be i nc l ude d in t he r e p r e s e n t a t i on . W e w i l l s t a r t w i t h t he h o w t ype

que s t i ons .

By a

method subroutine

I m e a n o n e w h i c h i n e f f e c t s a y s , y o u w a n t t o b r i n g

a b o u t s u c h a n d s u c h s t a te o f a f f a i r s , w e ll , I s u g g e s t u s in g t h e f o l l o w i n g m e t h o d .

T h e r e i s a s t a n d a r d w a y i n w h i c h s u c h m e t h o d s u b r o u t i n e s a r e i n d i c a t e d , a s f o r

e x am p l e in P L A N N E R .

( G O A L ( s o m e s ta te o f a ff ai rs ) ( U S E m e t h o d - n a m e ) )

H e r e m e t h o d - n a m e is th e n am e o f s o m e P L A N N E R t h e o re m w h i c h c a n b e u s ed

t o b r i ng a bou t t he de s i r e d s t a t e o f a f f a i r s . F u r t he r m or e , i t w i l l ha ve a theorem

pattern

w h i c h m a t c h e s ( in t h e t y p i c a l p a t t e rn m a t c h i n g s e n s e ) t h e

goal pattern

in

t he . a b o v e G O A L s t a te m e n t . A d o p t i n g t h i s n o ta t io n t o o u r s l i g h tl y d i f f e r e n t

s y n t a x , w e m i g h t s a y :

P A I N T I N G 3 7 ( all th e p a in t r e m o v e d f r o m i ns tr u m e n t)

u s e w a s h i n g - f r a m e

I n d e e d , w i t h t w o s m a l l c h a n g e s t h i s is w h a t I w il l d o . T h e f i r s t c h a n g e i s m i n o r ,

s im p l y b e in g t he r e p la c e m e n t o f th e w o r d u s e b y th e t e rm C O M E S - F R O M .


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362 EUGENE CHARNIAK

I n t h e a b o v e s i t u a t i o n t h i s m a k e s n o d i f f e r e n c e , a l t h o u g h m y r e p l a c e m e n t i s

a d m i t t ed l y s o m e w h a t le s s m n e m o n i c . ( O n e c a n t h in k o f it h o w e v e r a s i n d i c a ti n g

w h e r e th e d es ir e d s ta te o f a f fa i rs C O M E S - F R O M , o r e q u iv a l e n tl y , h o w i t i s to

c o m e a b o u t . ) H o w e v e r , t h e re a r e o t h e r c i r c u m s t a n c e s in w h i c h th e w o r d u s e

h a s u n d e si ra b le c o n n o ta t io n s w h i c h C O M E S - F R O M d o e s n o t s h a re . I n p a r ti c u -

l a r, u s e h a s t h e c o n n o t a t i o n o f a n a n i m a t e a g e n t w h o d e s i re s a p a r t ic u l a r

o u t c o m e . I n m a n y c a s e s w e w i ll w a n t t o e x p r e s s h o w a n o f te n u n d e s i ra b l e s ta t e

o f a f f a i r s i s t he r e s u l t o f s om e pu r e l y phys i c a l p r oc e s s . I n s uc h a c a s e w e c ou l d

s a y t h at th e s ta te o f af f a ir s C O M E S - F R O M t h e p h y s i c a l p r o c e s s , b u t n o t t h a t w e

u s e t h e p r o c e s s t o b r in g a b o u t th e s ta t e o f af f a ir s . ( O f c o u r s e , f r o m a p u r e l y

t e ch n i ca l p o i n t o f v i e w t he c o m p u t e r c o u l d n o t c ar e l e s s w h i c h t e r m w e u s e d . )

O n e s u c h e x a m p l e i s in v o l v e d i n t he c o m p l e t e s p e c i f ic a t io n o f a ru l e w e h a v e n o t

ye t i nc l ude d i n t he pa i n t i ng f r a m e :

P A I N T I N G 1 5 ( c o v er e v e ry t h in g w i th p a pe r)

H e r e e v e r y t h i n g o n l y i n c lu d e s t h in g s w e d o n o t w a n t s p o t te d w i t h p a i n t.

E ve n t ua l l y , w he n w e c om pl e t e l y s pe c i f y t h i s r u l e , w e w i l l s t a t e t ha t t he s po t t i ng

C O M E S - F R O M th e p ro ce ss es o f D R I P P I N G a nd S P L A S H I N G . T o sa y w e

u s e t he s e p r oc e s s e s t o c r e a t e spo t s , i n t h is c on t e x t , w ou l d be a b i t b i z a r r e .

T h e s e c o n d c h a n g e t o b e m a d e i n t h e P L A N N E R t y p e f o r m a l i s m i s m o r e

c om pl e x t ha n r e p l a c i ng one w o r d by a no t he r . A s I m e n t i one d e a r l i e r , the r e i s t he

c o n v e n t i o n in P L A N N E R t h at t h e p a t te r n o f t he t h e o r e m m u s t m a t c h th e g o a l

pa t t er n . I n t he c ou r s e o f m a k i n g t h is m a t c h one b i nds t he va r i a b l e s i n the t he o r e m

pa t te r n s o t he y r e f l e c t t he s pe c i a l s ta t e o f a ff a i r s m e n t i one d i n the goa l . T h a t i s , i f

ou r goa l is t o pu t b l oc k A on b l oc k B , o u r t he o r e m w i ll g i ve ge ne r a l i n s t ruc t i ons

f o r pu t t ing one b l oc k on a no t he r . T o s pe c i f y t h i s t o the c u r r e n t s i t ua t ion , w e

s i m p l y b i n d t h e a p p r o p r i a t e v a r i a b le s in t he p a t te r n t o b l o c k A a n d b l o c k

B , r e s p e c ti v e ly . G i v e n th a t t h e r e i s o n l y o n e p at te r n p e r t h e o r e m , b y s p e c i f y i n g

t he t h e o r e m n a m e in t he u s e s t a te m e n t w e a u t o m a t i c a l l y a r e s p e c i f y i n g t he

p a tt er n to b e m a t c h e d . ( O f c o u r s e , o n e c an c a ll a t h e o r e m i n P L A N N E R e n t i re l y

on t he ba s i s o f t he pa t t e r n w i t hou t a ny m e n t i on o f t he t he o r e m na m e a t a l l . Bu t

th i s i s bes ides the po in t in the cur ren t d i scuss ion . )

I n t he r e p r e s e n t a t i on p r e s e n t e d he r e t he r e i s no un i que t he o r e m pa t t e r n i n t he

s en s e r eq u ir ed b y t h e P L A N N E R m e c h a n i s m . I n st e ad t h er e m a y b e m a n y s ta te -

m e n t s in a f r a m e w h i c h s e r ve a s pa t t e r n s . ( I l l u s t ra t i ng t h is w o u l d t a ke u s t oo f a r

a f i e ld , bu t to the reader in te res ted in re turn ing to th i s po in t , no te ( see F ig . 4 and

7 ) t ha t in S T I C K , S T I C K 6 , 8 , a n d 1 0 s e rv e a s p a t t e r n s f o r P A I N T I N G 2 2 ,

P A I N T I N G 2 6 , a n d P A I N T I N G 1 7 , r e s p e c ti v e ly . ) T h e p o i n t h e r e is t ha t i f w e

a r e t o g i ve up a s pe c i a l a nd un i que pa t t e r n , w e m us t i nd i c a t e w ha t i s t o be

m a t c h e d b y s o m e o t h e r m e a n s .

A b i t o f t e r m i n o l o g y w o u l d b e u s e fu l in t h is r e g a r d . F r a m e s t a t e m e n t s , o r

s i m p l y s t a t e m e n t s , a r e t h o se t h in g s , l ik e P A I N T I N G 3 7 , th a t w e u s e t o b u i ld

up ou r f r a m e s . T h e y i nva r i a b l y ha ve a p r e d i c a t e p l u s a r gum e n t s t r uc tu r e , t hus f a r


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A FRAMED PAINTING 363

presented by English phrases in parentheses, (al l the paint removed from in-

strument), which we will call the b od y of the frame statement. The state-

ment may also have other parts, such as a name, PAINTING37, or tags like

C O M E S - F R O M which we are currently in the process of introducing. Given

this terminology, our COMES-FROM tag must somehow indicate the frame

statement body which is to serve as the matching pattern. I will indicate the

appropriate frame statement in the most obvious way, by giving its name. (As I

just did here, I shall frequently refer to a frame statement body as simply a frame

statement in which no confusion will result.)

With the two changes described above, our representation for PAINTING37

becomes:

PA IN TI NG 37 (all paint removed from instrument)

COMES-FROM: (WASH-GOAL)

Here WASH-GOAL is the name of the particular statement in the WASH

frame. Its body, of course, must match the body of PAINTING37.

To give another example of the same construction, we must have a rule in

PA INT IN G to the effect that one should not have too much paint on the painting

instrument, and that a good way to prevent this is to remove excess liquid by

pressing the instrument against a solid surface, causing some liquid to drip off.

We will call this procedure for the removal of liquids REM-LIQand our addition

to PAINTING will be:

PA IN TI N GI 9 (not too much paint on instrument)

COMES-FROM: (REM-LIQ-GOAL)

Let us give one last example of the use of COMES-FROM, this one of a

different sort. So far we have used our COMES-FROM pointers to indicate a

complex activity, like washing or removing liquids from an absorbant material.

We can also use it to indicate the physical process which underlies these ac-

tivities. So we are told in PA INTING I7 to get paint on the painting instrument,

but so far we have not indicated the physical process which allows us to do so.

This physical process, which we will call STICK, has its own frame, which as a

first approximation might look like Fig. 4.

In effect this says that if a solid comes in contact with sufficient liquid some of

FIG. 4

Stick try 1

EVENT

: I--STICK6 liquid in contact with object)

|WITH-OPTIONAL-CONDITIONS

I(STICK8 (amount of liquid is greater than some constant) )

[CAUSES

~'IF STICK8 THEN STICKI0 (liquid sticks to object)

ELSE STICK I I (liquid sticks to part of object)

STICK try I.


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364

E U G E N E C H A R N I A K

th e l iq u id w i ll s ti ck to .th e s o li d . T h e O P T I O N A L - C O N D I T I O N S a r e n o t

p r e r e qu i s i t e s o f t he e ve n t , bu t m a y a f f e c t t he e nd r e s u l t . - I n t h i s c a s e i f t he r e i s

l e s s l iqu i d on l y pa r t o f t he s o l id w i ll be c ove r e d . W e c a n r e l a t e th i s phys i c a l

m e c h a n is m to P A I N T I N G I 7 in th e f o ll o w in g w a y :

P A I N T I N G I 7 ( g et p a in t o n t he p a in t in g i n st ru m e n t )

C O M E S - F R O M : ( S T I C K I 0 )

( A g a in , t he b od ie s o f S T I C K I 0 a n d P A I N T I N G 1 7 m u s t m a t c h . T h e c u r re n t

E ng l i s h e xp r e s s i ons do no t , bu t t h i s w i l l be i r one d ou t w he n w e m ove i n t o t he

c o m p l e t e f o r m a l is m . )

W i t h t h e c h a n g e s s u g g e s t e d i n t h i s s e c t i o n , o u r P A I N T I N G n o w l o o k s l i k e

F ig . 5 .

1 .3 R e a s on s a n d L E A D S T O

I n m y o r i g i n a l c o m m e n t a b o u t w a n t i n g a r e p r e s e n t a t i o n w h i c h e n c o u r a g e s a

de e p unde r s t a nd i ng o f t he t op i c I s ugge s t e d t ha t i t w a s no t s u f f i c i e n t t ha t t he

p r o g r a m k n o w th a t t he b r us h o r w h a t e v e r sh o u ld b e w a s h e d - - i t m u s t a ls o k n o w

how t o do i t , a nd w hy i t s hou l d be done . I n t he l a s t s e c t i on w e c ons i de r e d t he

f o r m e r a s pe c t o f t he p r o g r a m , n ow l e t u s t u rn t o t he l a tt e r.

I n C h a r n i a k ( 1 9 75 ) I c o m m e n t e d t h at m u c h o f t h e in f o r m a t i o n w e h a v e a b o u t

a c t iv i t ie s i s i n t he f o r m o f s u gg e s t i o ns r a t he r t ha n s t r ic t l y ne c e s s a r y a c t i v i t ie s .

I no t e d t he r e t ha t e a c h s ugge s t i on ha d a r e a s o n a s s oc i a t e d w i t h i t w h i c h

e x p l a i n e d w h y t h e s u g g e s t i o n s h o u l d b e f o l l o w e d . W a s h i n g a b r u s h ( P A I N T -

I N G 3 7 ) i s a c l e a r - c u t e x a m p l e , a n d t h e r e a s o n i s s i m p l y t h a t o t h e r w i s e t h e

b r us h w i ll be c o m e s t if f a nd una bs o r ba n t . I a m no l on ge r c onv i nc e d t ha t t he r e i s a

c l e a r- c u t c l a ss o f s u g g e s t i o n s , f o r o n c l o s e i n s p e c ti o n t h e y t e n d t o m e r g e w i th

s t r i c t r e qu i r e m e n t s . Bu t t he no t i on t ha t s om e f r a m e s t a t e m e n t s s hou l d ha ve

r e a s ons a s s oc i a t e d w i t h t he m s e e m s una s s a i l a b l e t o m e , a nd i t i s t h i s a s pe c t

which wi l l be d i scussed he re .

P A I N T I N G t r y 2

G O A L : P A I N T I N G - G O A L o b j ec t t o b e p a i n t ~ h a s a c o a t o f p a in t o n i t)

E V E N T : P A I N T I N G 1 4 o b j ec t i s n o t d i rt y )

P A I N T I N G I 5 e v e r yt h in g c o v e r e d w i th p a p er )

P A I N T I N G I 6 L O O P

P A I N T I N G I 7 g e t p a i nt o n t h e p a i n t in g i n s tr u m e n t )

C O M E S - F R O M : S T I C K I 0 )

P A I N T 1 N G I 9 n o t t o o m u c h p a in t o n i n st ru m e n t )

C O M E S - F R O M : R E M - L I Q - G O A L )

P A I N T I N G 2 2 b r i n g i n s t r u m e n t i n c o n t a c t w i t h o b j e c t )

)

a l l pa i n t r e move d f rom pa i n t i ng i n s t rume n t )

C O M E S - F R O M : W A S H - G O A L )

P A I N T I N G 3 7

F I G . 5 P A I N T I N G t ry 2 .


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A FRAM ED PAINTING 365

O f c o u r s e , P A I N T I N G 3 7 ( al l p a i nt r e m o v e d f r o m i n st r u m e n t) i s n o t t he o n l y

f r a m e st a te m e n t in P A I N T I N G t h at c o u l d u s e a n a ss o c ia t e d re a s o n . T w o o t h e r s

are :

P A I N T I N G I 4 ( o b je c t is n o t d ir ty )

r e a s o n : o t h e r w i s e p a i n t m a y f l a k e a n d c r a c k .

P A I N T I N G 1 9 ( no t to o m u c h p a in t o n i ns tr u m e n t)

r e a s on : o t he r w i s e t he pa i n t w i l l d r i p .

N o w r e p r e s e n t i n g t h e s u g g e s t i o n s i s n o p r o b l e m . W e h a v e a l r e a d y s e e n t h a t t h e y

c a n b e h a n d l e d m u c h l i k e a n y o t h e r f l a m e s t a t e m e n t . T h e d i f f i c u l t y c o m e s i n

ha nd l i ng t he r e a s ons f o r t he s ugge s t i ons .

O n e p o s s i b i li t y w o u l d b e s i m p l y t o i n c lu d e t h e s e r e a s o n s t a t e m e n t s in t h e

r e p r e s e n t a t i on , m uc h l ike I d i d a bo ve , a l t houg h na t u r a l l y no t i n E ng l i s h s e n -

t e n c e s. T h i s , h o w e v e r , i s i n s u f f ic i e n t b y i t s el f , b e c a u s e it d o e s n o t g o f a r e n o u g h

in r e p r e s e n ti n g o u r c o m p l e t e u n d e r s t a n d i n g o f th e s i tu a t io n . S o , c o n s i d e r t h e

f o l l ow i ng s t o r y :

J a c k h a d f i n is h e d p a i n t in g . F a t h e r a s k e d h i m i f h e w a s h e d t h e b r u s h . J a c k

s a id N o , b u t M o t h e r c a ll e d m e f o r l u n c h , s o I l e ft t h e b r u s h in th e p a i n t

a n d w i l l w a s h t h e b r u s h l a t e r .

T o u n d e r s t a n d w h y J a c k h a d a n a c c e p t a b l e a n s w e r r e q u i r e s k n o w i n g t h a t t h e

c r uc i a l p r ob l e m w i t h pa i n t on t he b r u s h i s t ha t t he pa i n t w i l l d r y , a nd t h i s i n t u r n

l ea d s t o th e p r o b l e m o f st i ff a n d u n a b s o r b a n t b r u s h e s . F u r t h e r , w e m u s t k n o w

t ha t d r y i ng r e qu i r e s e x po s u r e t o a i r, a n d i f t he b r u s h i s in t he pa i n t i t i s no t

e x p o s e d t o a ir . T h i s w o u l d s e e m t o i m p l y t h a t w e s h o u l d i n c lu d e in o u r re a s o n a ll

s o r t s o f i n f o r m a t i o n a b o u t w h a t h a p p e n s w h e n p a i n t d r i e s . B u t c l e a r l y w e n e e d

t h i s know l e dge i n o t he r s i t ua t i ons a l s o ( pa i n t d r i e s on o t he r t h i ngs be s i de s pa i n t

b r u sh e s ) s o w e s h o u ld p r e s u m a b l y p u t it i n to i ts o w n s e p a r a t e f r a m e , P A I N T -

D R Y . S p a c e e c o n o m y a r g u e s t h a t t h i s i n f o r m a t i o n s h o u l d n o t b e r e p l i c a t e d

e l se w h e r e , s o w e m u s t s o m e h o w u t il iz e P A I N T - D R Y in o u r e x p l ic a t io n o f t h e

PAINT-DRY

EVENT

FIG. 6

: I---PAINT-DRY2 AN D PAIN T-DR Y3 (paint on object)

| PAIN T-DR Y4 (liquid gone leaving residue)

| COM ES-FROM : (evaporation))

[WITH-OPTIONAL-CONDITIONS

[(PA IN T- DR Y 6 (object is absorbant)

| C A U S E S

t.-PAINT-DRY7

(AND PAIN T-DR Y8 (residue part of object)

(IF PAINT-DRY6

TH N (AND PAIN T-DR Y10 (object is no longer absorbant)

PA INT -DR YI 1 (object is no longer flexible) ) ) )

PAINT-DRY.


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366

EUGENE CH RNI K

r e a s ons f o r w a s h i ng . T o s e e how t h is c ou l d be don e , l e t u s ta ke a l ook a t t h i s ne w

f r a m e .

T h i s a g a i n i s n o t c o m p l e t e , b u t f o r o u r p u r p o s e s w e o n l y n e e d t o n o t e t h a t

P A I N T I N G 3 7 c a ll s f o r a s i tu a t io n w h i c h i s in d i r ec t ly o p p o s e d t o t h a t c a l le d f o r

in P A I N T - D R Y 3 , a s s u m i n g o f c o u r s e w e i d e n t if y th e p a in t in g i n s t r u m e n t in

P A I N T I N G 3 7 w ith th e o b je ct in P A I N T - D R Y 3 . T h e re as on f o r P A I N T I N G 3 7

t h e n i s t o p r e v e n t P A I N T - D R Y f r o m o c c u r r i n g o n t h e i n s t r u m e n t a n d h e n c e

p r e v e n t i n g t h e u n d e s i r a b l e r e s u l t s w h i c h P A I N T - D R Y c a n c a u s e . T o p u t t h i s

s li gh tl y d i ff e re n t ly , w e d o P A I N T I N G 3 7 b e c a u s e it L E A D S - T O t h e n e g a t io n o f

P A I N T - D R Y 3 a n d h e n c e t h e n o n o c c u r r e n c e o f P A I N T - D R Y . T h i s i n t u r n

s ugge s t s c a s t i ng ou r f r a m e s t a t e m e n t a s f o l l ow s :

P A I N T I N G 3 7 ( N O T ( p ai nt o n p a in t in g i n st ru m e n t )

L E A D S - T O : ( P A I N T - D R Y 3 ) )

C O M E S - F R O M : ( W A S H - G O A L )

A s b e f or e , th e C O M E S - F R O M e x p la in s h o w P A I N T I N G 3 7 is to b e a c h ie v e d .

T h e L E A D S - T O , o n th e o t h e r h a n d , is a t t a c h e d t o t he i n n er s t at e m e n t ( p a in t

on pa i n t ing i n s tr um e n t ) a nd s a ys t ha t if one d oe s l e a ve t he pa i n t on , o ne m i gh t

h a v e p r o b l e m s w i t h t h e p a i n t d r y i n g , p r o v i d e d t he o t h e r p r e r e q u i s i te s t o

P A I N T - D R Y a r e s a t i s f i e d .

A r e a s o n t he n is a de s c r i p t i on o f t he e ve n t s t ha t w i l l oc c u r , o r f a i l t o oc c u r ,

i f t he s ugge s t ion i s c a r d e d ou t . W e a c c e s s t h i s de s c r i p t i on by a po i n t e r t o the

f r a m e de s c r i b i ng t h i s e ve n t , a nd i n pa r t i c u l a r t o t he f r a m e s t a t e m e n t w h i c h t he

s ugge s t i on t e l l s u s e i t he r t o a c h i e ve , o r t o m a ke s u r e ne ve r t a ke s p l a c e . T h i s

p o in t er is m a r k e d b y t he s y m b o l L E A D S - T O r a t he r t ha n , s a y , r e a s o n f o r

m u c h t he s a m e r e as o n t ha t w e u s ed C O M E S - F R O M r a th e r t ha n u s e . T h e r e

a re c a s e s in w h i c h r e a s o n h a s u n a c c e p t a b l e a n t h r o p o m o r p h i c c o n n o t a t i o n s , as

f o r e x a m p l e in P A I N T I N G 3 7 i ts el f. I t w o u l d h a rd l y d o to sa y th a t t he r e a s o n

( o r g o a l ) f o r l e a v i ng the pa i n t on i s t o a l l ow i t t o d r y . ( N o t e t ha t the u s e o f

G O A L in t he r e p r e s e n t a t i on ( se e F i g . 5 )

s

t e l e o l og i c a l i n na t u r e , a l t hough m uc h

o f th e d i ff e re n c e b e t w e en L E A D S - T O a n d G O A L is sy n t ac t ic i n n a tu r e .)

I h a v e i nt ro d u ce d L E A D S - T O a s a w a y o f i nd ic a ti ng r e a s o n s b e c a u s e t h at

w a s m y i ni ti al m o t i va t i on , a nd i t s e e m e d t he m o~t in t u i t ive l y s t r a i gh t f o r w a r d w a y

t o e x p l a in t h e m . T h e r e i s , h o w e v e r , a p o s s ib l e m i s u n d e r s ta n d i n g s t e m m i n g f r o m

t hi s a b o u t w h i c h t he r e a d e r s h o u ld b e w a r n e d . S i n c e r e a s o n s a s I h a v e b e e n

us i ng t he t e r m a r e c a us a l r e l a t i ons , t he r e i s a t e m p t a t i on t o i n t e r p r e t A L E A D S -

T O B a s A C A U S E S B . T h i s t em p t a ti o n s h ou l d b e a v o id e d . A L E A D S - T O

po i n t e r doe s no t i t s e l f i nd i c a t e c a us a t i on , bu t r a t he r po i n t s t o w he r e r e l e va n t

c a u s a l i n f o r m a t i o n c a n b e f o u n d . A p a r a l l e l s t a t e m e n t c a n b e m a d e a b o u t

C O M E S - F R O M , bu t its in tr od u ct io n v i a P L A N N E R u s e s ta te m e n ts d o e s

no t s e e m t o i nv i t e t he pa r a l l e l m i s unde r s t a nd i ng .

T o g i v e a n o t h e r e x a m p l e o f a L E A D S - T O t a g , t h e f r a m e w h i c h d e s c r i b e s a

d r i p s t a te s t ha t one o f t he p r e r e qu i s i t e s f o r d r i pp i ng i s t he p r e s e n c e o f s u f f i c i e n t


13/40

A F RA M E D P A IN T IN G 367

f l u i d s t i c k i n g t o a s u r f a c e . S o D R I P 3 i n t h e n e x t e x a m p l e s t a t e s t h a t t h e v o l u m e

o f t hi s f l u id m u s t b e g r e a t e r th a n s o m e t h r e s h o l d . I t i s t h is p r e r e q u i s i t e w h i c h w e

n e g a te in P A I N T I N G 1 9 ( n o t t o o m u c h p a i n t o n i n st r u m e n t ) a n d w e w i ll i n d ic a te

th i s by :

P A I N T I N G I 9 ( N O T ( G R E A T E R am o u nt o f p ain t o n i n st r um e nt

D R I P - C O N S T )

L E A D S - T O : ( D R I P 3 ) )

I h a v e s ta r te d in P A I N T I N G I 9 t o p u t th e b o d y o f t h e st a t em e n t i n to f o r m a l i s m

s o a s t o b e t te r i n d ic a te th e c o r re s p o n d e n c e b e t w e e n w h a t P A I N T I N G 1 9 r e q u i r e s

a n d w h a t D R I P r e q u i r e s .

W e n o te d a t t he en d o f S e c t io n 1 .2 th a t t he C O M E S - F R O M t a g c o u l d b e u se d

t o r e l a t e a n a c t i v i t y t o i t s u n d e r l y i n g p h y s i c a l p r o c e s s e s . T h e s a m e i s t r u e o f

L E A D S - T O . W i th in P A I N T I N G t h er e a re s e ve r al e x a m p l e s o f th is , o n e o f

w h i c h w e h a v e n o t y e t i n c l u d e d i n o u r p a i n t i n g f r a m e :

P A I N T I N G 2 6 ( G R E A T E R a m o u n t o f p a in t o n in s t r um e n t

C O A T - C O N S T )

T h e r e a s o n w e i n si st o n P A I N T I N G 2 6 i s t h at o th e r w i s e t h e p a i n t w i ll n o t c o v e r

t he p o r ti o n o f th e o b j e c t w i th w h i c h t h e i n s t r u m e n t c o m e s in c o n t a c t . T o p u t t h is

s li g ht ly d i ff e r en t ly , P A I N T I N G 2 6 e n s u r e s t ha t S T I C K 8 ( se e th e s t i c k i n g r u le a t

t he e n d o f S e c t io n . 2 ) i s s a t is f ie d . W e c a n i n d ic a t e t h is b y a d d i n g t o P A I N T -

I N G 2 6

L E A D S - T O : ( S T I C K 8 )

( T ha t t h i s l e a ds t o t he pa i n t be i ng on t he object a s o p p o s e d t o t h e i n s t r u m e n t o r

e l s e w h e r e i s a p r o b l e m w h i c h w i l l b e d e a l t w i t h i n S e c t i o n 2 . 3 . ) A n o t h e r e x a m -

p le o f th e us e o f L E A D S - T O is P A I N T I N G 2 2 ( b ri ng t h e i n st ru m e n t in co n t a ct

w i t h t h e o b j e c t ) . T h i s g u a r a n t e e s t h a t S T I C K 6 i s s a t i s f i e d , a n d h e n c e s h o u l d b e

s im i l ar ly m a r k e d . T h e s e c h a n g e s h a v e b ee n m a d e in F i g . 7 ( P A I N T I N G t ry 3 ).

1.4 Intermediar ies and M atching

T h e s k e p t i c a l r e a d e r , t h a t i s , t h e o n e w h o c h e c k s e v e r y e x a m p l e t o m a k e s u r e

t h ey a r e a s th e a u t h o r c l a i m s , m a y h a v e n o t i c e d t h a t s o m e o f th e r e c e n t e x a m p l e s

u s in g L E A D S - T O p o i n te r s s im p l y d o n o t w o r k , a t l e a st n o t in th e w a y e x p l a i n e d

in th e p a p e r . T o s e e th i s , t h e r e st o f u s m u s t b e a b i t m o r e s k e p t ic a l o u r s e l v e s ' a n d

l o o k . a t p r e c i s e l y w h a t i s b e i n g d o n e . W e h a v e i n t r o d u c e d t h e f o l l o w i n g i n t o

P A I N T I N G :

P A I N T I N G 2 2 ( b ri n g i n s tr u m e n t in c o n t a c t w i th o b j e c t)

L E A D S - T O : ( S T I C K 6 )

L o o k i n g b a c k t o t h e s t i c k i n g f r a m e w e f i n d :

S T I C K 6 ( L i q u i d in c o n t a c t w i th o b j e c t)


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3 6 8 E U G E N E C H A R N I A K

P A I N T I N G t r y 3

G O A L : P A I N T I N G - G O A L ( o b je c t t o b e p ai n te d h a s a co a t o f p a in t o n it)

E V E N T : - P A I N T I N G I 4 ( N O T ( o b je c t d ir ty )

- P A I N T I N G I 5

- PAINTING 16

- - P A I N T I N G 3 7

L E A D S - T O : ( D I R T Y - O B J 3 )

(eve ry t h i ng i s cove red w i t h pape r )

( L O O P

- P A I N T I N G I 7 ( g e t p a in t o n t h e p a i n ti n g i n s tr u m e n t )

C O M E S - F R O M : ( S T I C K I 0 )

P A I N T 1 N G I 9 ( N O T ( G R E A T E R a m o u n t o f p a in t o n i ns tr

D R 1 P - C O N S T )

L E A D S T O : ( D R I P 3 ) )

C O M E S - F R O M : ( R E M - L I Q - G O A L )

- ' P A I N T I N G 2 2 ( b r in g i n s tr u m e n t i n c o n t a c t w i t h o b j e c t)

L E A D S - T O : ( S T I C K 6 )

( D U R I N G P A I N T I N G 2 6 P A I N T I N G 2 2 )

- P A I N T I N G 2 6 ( a m o u n t o f p a i n t o n in s t ru m e n t i s g r e a te r

t han some cons t an t )

L E A D S - T O : ( S T I C K 8 )

)

(NOT (pa i n t on pa i n t i ns t rument )

L E A D S - T O : ( P A I N T - D R Y 2 ) )

C O M E S - F R O M : ( W A S H - G O A L )

F I G . 7 P A I N T I N G t ry 3 .

T h e p r o b l e m h e r e is t h e r e q u i r e m e n t t h a t i f w e h a v e

F R A M E - S T A T E M E N T I b o d y o f f ra m e s ta te m e n t 1)

L E A D S - T O : F R A M E - S T A T E M E N T 2 )

t he n th e b o d i e s o f f r a m e s t a t em e n t s o n e a n d t w o m u s t m a t c h . N o w g i v e n m y

p r o p e n s i t y t o e x p r e s s t h e b o d i e s i n f o r m a l l y w i t h a n E n g l i s h p h r a s e , i t i s h a r d t o

d e c i d e p r e c is e l y w h e n t w o s u c h b o d i e s d o m a t c h , b u t i t s h o u l d b e c l e a r e n o u g h in

th is c a s e th a t P A I N T I N G 2 2 a n d S T I C K 6 d o n o t - - a p a in t i ng i n s t ru m e n t i s a

s o l i d n o t a l i q u i d .

O f c o u r s e , i t i s c l e a r w h a t i s h a p p e n i n g h e r e . B y t h e t i m e w e r e a c h P A I N T -

I N G 2 2 w e h a v e p a in t o n o u r i n s t r u m e n t , s o it i s t he p a i n t w h i c h c o m e s i n c o n t a c t

w i t h t h e o b j e c t , a n d i t i s t h e p a i n t w h i c h s h o u l d b e m a t c h e d a g a i n s t t h e l i q u id in

S T I C K 6 . S o P A I N T I N G 2 2 a nd S T I C K 6 c a n b e m a d e to m a t c h i f w e s o m e h o w

u s e t h e a u x i li a ry r u le f o u n d i n F i g . 8 w h e n m a k i n g t he m a t c h . T h e r e a d e r m a y

h a v e n o t e d t h a t I u s e d a n a r r o w h e r e t o i n d i c a t e a n i m p l i c a t i o n , w h e r e a s e a r l i e r

t h e y w e r e u s e d t o in d i c a t e t i m e s e q u e n c e s . I n f a c t , t h e a r r o w s r e a l l y in d i c a t e

S T I C K Y - O N 6 ( A N D S T I C K Y - O N 7 ( S T I C K - O N L I Q S U R )

I M P L IE S S T IC K Y - O N 9 ( C O N T A C T S U R O T H E R - S U R ) )

S T 1 CK Y - O N I0 ( C O N T A C T L IQ O T H E R - S U R )

FIG. 8 A re l a ti on i n t he STIC KY -ON f rame .


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A F R A M E D P A I N TI N G 6 9

n o t h i n g a s t h e y a r e e n t i r e ly s u p e r f l u o u s a n d n o t s e e n b y t h e m a c h i n e a t a ll . I h a v e

i n c l u d e d t h e m s i m p l y a s m e a n s t o p r o v i d e s o m e v i s u a l b r a c k e t i n g . )

I h a v e u s e d t h e f u l l f o r m a l i s m i n F i g . 8 b e c a u s e , a s w e h a v e s e e n , i n f o r m a l

E n g l i s h m a k e s i t d i f f i c u l t t o d e c i d e p r e c i s e l y w h e n t w o s t a t e m e n t s m a t c h . T h e

e s s e n c e o f t h is r u le s h o u l d b e c l e a r e n o u g h , h o w e v e r . I f a li q u id i s s t i c k in g t o a

s u r f a c e , a n d a s e c o n d s u r f a c e c o m e s i n c o n t a c t w i t h t h e f i r s t , t h e n i t a l s o c o m e s

in contac t w i th the l iqu id .

I n t u it i v el y th is r u le i s p a r t o f w h a t w e m e a n w h e n w e s a y a l iq u id i s S T I C K Y -

O N a su r f a c e . T h e r e a r e n a t u r a ll y o t h e r s u ch r u l es ; f o r e x a m p l e , i f s o m e t h i n g i s

s t i c k i ng t o a s u r f a c e , t he n t he s u r f a c e s up po r t s i t. O r a ga i n , t o s ti c k i s t o s t i c k on

t he e x t e r i o r o f t he o b j e c t , a n d in a s e n s e , t o b e c o m e p a r t o f t h a t e x t e r i o r . A n d n o

d o u b t t h e r e a r e m a n y m o r e . T h e s e r u l e s a r e g a t h e r e d t o g e t h e r i n t h e S T I C K Y -

O N f r a m e . N e e d l e s s to s a y , S T I C K Y - O N i s a s ta te , n o t a n a ct io n l i ke p a i n t in g

a n d a ll o f th e o t h e r s w e h a v e l o o k e d a t s o f a r , a n d n a t u r a l ly s t a t e f r a m e s w i ll h a v e

s o m e w h a t d i f f e r e n t p r o p e r t i e s f r o m a c t i o n f r a m e s . O n e s u c h d i f f e r e n c e i s t h e

p r e s e n c e o f r u l es l i k e th e o n e p r e s e n t e d a b o v e . I n S e c t io n 2 o f th i s p a p e r , w e w i l l

d i s c u s s s t a t e f r a m e s i n d e t a i l, b u t f o r t h e m o m e n t w e s i m p l y n e e d a w a y t o

i nd i c a t e t ha t t h i s r u l e s e r ve s a s a n

intermedi ry

b e tw e en P A I N T I N G 2 2 a nd

S T I C K 6 . W e w i l l d o t h i s a s f o l l o w s :

P A I N T I N G 2 2 C O N T A C T A B - S U R - P A R T S U R F A C E - P A R T )

L E A D S - T O : S T I C K Y - O N 9 S T I C K Y - O N 1 0 S T I C K 6 )

A B - S U R - P A R T i s p a r t o f t h e a b s o r b a n t s u r fa c e o f t he p a in t i n g i n s t ru m e n t ,

w h i le S U R F A C E - P A R T is p a rt o f th e su r fa c e o f th e th in g b e i n g p a in t e d .)

I n th is r e pr e se n ta ti o n S T I C K Y - O N 9 S T I C K Y - O N 1 0 ) a r e to b e in t er p re te d as

f o ll o w s : t o t r a n sf o r m o u r s ta r ti n g p o i n t P A I N T I N G 2 2 ) i n to o u r e n d p o i n t

S T I C K 6 ) , f ir st m a t c h th e s ta r ti n g p o in t w i th S T I C K Y - O N 9 t h en u t il iz e t he r u le

w h ic h c o nn e ct s S T I C K Y - O N 9 to S T I C K Y - O N I 0 , a n d m a tc h S T I C K Y - O N 1 0

a g a in s t t h e e n d p o i n t S T I C K 6 ) .

O n e c o u l d , o f c o u r s e , n o t in c l u d e i n t e r m e d i a r i e s in t h e r e p r e s e n t a t i o n a n d

i n st e ad e x p e c t t h e p r o g r a m t o l o c a t e th e a p p r o p r i a t e r u l e w h e n m a k i n g t h e m a t c h .

I h a v e n o t t a k e n t h i s a p p r o a c h b e c a u s e i t s e e m s t o m e t h a t i t i s w o r t h t h e e x t r a

s p a c e i n o r d e r t o s a v e t h e e x t r a t i m e n e e d e d t o s e a r c h f o r t h e a p p r o p r i a t e i n t e r -

m e d i a r i e s b e t w e e n o u r s t a r t i n g a n d f i n i s h i n g p o i n t s . T h i s w i l l b e c o m e e v e n

c l e a r e r w h e n w e n e e d t w o o r t h r e e i n t e r m e d i a r y p a i r s t o m a k e t h e t r a n s i t i o n .

I n d e e d , l et u s c o n s i d e r s u c h a c a s e n o w . T h e e x a m p l e i s t h e ru l e w e i n t r o d u c e d

s a y i n g th a t th e a m o u n t o f p a i n t o n t h e p a i n t i n g i n s t r u m e n t s h o u l d n o t e x c e e d a

c e r t a i n th r e s ho l d f o r f e a r o f d r i pp i ng . A s l a s t se e n i n F i g . 7 i t l oo ke d l i ke :

P A I N T I N G 1 9 N O T G R E A T E R a m o u n t o f p ain t o n i ns tr um e n t

D R I P - C O N S T )

L E A D S - T O : D R I P 3 ) )

C O M E S - F R O M : R E M - L I Q - G O A L )


16/40

370 EUGENE CHARNIAK

W e h a v e n o t s p e c i f i e d t h e p r e c i s e f o r m o f R E M - L I Q - G O A L , b u t t h e g e n e r a l

i d e a o f R E M - L I Q i s t o d e s c r i b e h o w o n e u s e s p r e s s u r e o n a n a b s o r b a n t o b j e c t

( l ike a d ish c lo th) to dec rease the l iqu id in i t . As a f i r s t approximat ion then , the

g o a l o f R E M - L I Q w o u l d b e :

R E M - L I Q - G O A L ( C H A N G E L I Q - V O L a m o u nt N E G A T I V E )

whic h i s i n t e nde d to me a n tha t t he l i qu id vo lume c ha nge s ne ga t ive ly by some

a moun t .

C l ea rl y P A I N T I N G 1 9 d o e s no t in fa c t m a tc h R E M - L I Q - G O A L , a nd to

ma k e the m m a tc h we ne e d th r e e s e pa ra t e r e l a t ions . On e o f t he se is s e e n in F ig . 9 .

Th i s r u l e s a ys t ha t i f a t h ing inc r e a se s ( de c r e a se s ) i t ma y inc r e a se ( de c r e a se )

su f f i c ie n t ly t o be c om e g r e a t e r ( l es s ) t ha n a g ive n a m oun t . I n the s i t ua t ion a t ha nd

t hi s m e a n s t h a t w e c a n u s e R E M - L I Q t o d e c r e as e th e l i qu i d v o l u m e s u f f i c ie n t l y

t o p r ev e n t d r ip p i n g . B u t n o t e - - a n d t h is i s o n e o f t h e b e n e f i ts o f r e q u i ri n g e x p l i c i t

m a t c h i n g - - b e c a u s e t h e c h a n g e r u l e o n l y w o r k s s o m e t i m e s ( t h e v a l u e c o u l d

c ha nge , bu t i n su f f i c i e n t ly to r a i s e i t a bov e a g ive n th r e sho ld ) i t a u tom a t i c a l ly t e ll s

u s t h at th e u t il iz a ti o n o f R E M - L I Q d o e s n o t g u a r a n t e e f u l fi l lm e n t o f o u r g o a l . I t

i s some wha t s imi l a r t o t he s i t ua t ion w i th b r ing ing the i n s t r ume n t i n to c on ta c t

w i t h t h e o b j e c t - - a s t h e ru l e o f S T I C K Y - O N e x p l a i n s , th e r e m u s t b e p a i n t o n t h e

in s t r ume n t t o ma ke e ve r y th ing wor k a s de s i r e d . ( A l though in bo th c a se s t he

e nv i s ione d p r og r a m to u se t he se r u l e s wou ld a s sume the y we n t t h r ough un le s s

t o l d o t h e r w i s e . ) S o w e c a n c h a n g e P A I N T I N G 1 9 t o r e a d :

C O M E S -F R O M : ( C H A N G E 5 C H A N G E 2 R E M - L I Q - G O A L )

B u t t h i s i s s t i l l no t qu i t e r i gh t , a s we c a n se e by c ompa r ing the bod ie s o f

P A I N T I N G I 9 a n d C H A N G E 5 .

P A I N T I N G I 9 ( N O T ( G R E A T E R am o u n t o f p ain t o n in stru m en t)

C O N S T A N T ) )

C H A N G E 5 ( G R E A T E R X T H I N G )

Th i s , ho we ve r , c a n be c o r r e c t e d by a s e c ond in t e r m e d ia r y shown in F ig . 10 .

T h i s r u l e w h i c h h e l p s d e f i n e G R E A T E R c a n b e u s e d i n o u r i n t e r m e d i a r y a s

fo l lows:

C O M E S - F R O M : ( G R E A T E R 5 G R E A T E R I C H A N G E 5 C H A N G E 2

R E M - L I Q - G O A L )

FIG. 9

CHANGE2 (CHANGE THING AMOUNT SIGN)

IMPLIES (SOMETIMES)

CHANGE3 (IF (EQUAL SIGN POSITIVE)

THEN CHANGE4 (GREATER THING X)

ELSE CHANGE5 (GREATER X THING) )

A relation in the CHANGE frame.


17/40

A F R A M E D P A I N TI N G

G R E A T E R 1 ( G R E A T E R A B )

I F F

G R E A T E R 2 ( A N D G R E A T E R 3 ( N O T G R E A T E R 4 (G R E A T E R B A ) )

G R E A T E R 5 ( N O T G R E A T E R 6 ( E Q U A L A B) ) )

F I G . 1 0 A G R E A T E R r e la t io n .

371

A n d , in f a c t , e v e n th i s is n o t c o m p l e t e , b u t th e g e n e r a l i d e a o f h o w i n t e r m e d i a r y

r u l e s l i nk up i n c ha i n s s hou l d by t h i s po i n t be s u f f i c i e n t l y c l e a r t o m a ke ye t

a n o t h e r e x a m p l e u n n e c e s s a r y . ( T h e m i s s i n g r u le w o u l d r e la t e t h e a m o u n t o f p a i n t

a b s o r b e d b y t h e i n s t r u m e n t t o t h e a m o u n t o n t h e s u r f a c e , w h i c h i s a c t u a l l y

r e s p o n s i b l e f o r d r i p p i n g . )

L e t u s st e p b a c k a s e c o n d a n d t a k e a f r e sh l o o k a t w h a t w e a r e d o i n g w i t h o u r

i n t e r m e d i a r i e s . S u p p o s e w e h a v e :

F R A M E - S T A T E M E N T I ( . . . )

L E A D S - T O : ( I N T I . . . I N T n F R A M E - S T A T E M E N T 2 )

o r , f o r o u r c u r r e n t d i s c u s s i o n , t h e e q u i v a l e n t

F R A M E - S T A T E M E N T 2 ( . . . )

C O M E S - F R O M : ( IN T n . . . I N T I F R A M E - S T A T E M E N T 1 )

I n b o t h c a s e s w e a r e m a k i n g t h e f o l l o w i n g c l a i m :

G i v e n t h e s i t u a t i o n d e s c r i b e d i n f r a m e - s t a t e m e n t 1 , a n d g i v e n c e r t a i n o t h e r

c o n d i ti o n s, a s in d ir e ct ly s p e c if ie d b y I N T l . . . I N T n , a n d a ll o f t h es e h o l d a t t h e

s a m e t i m e T t h e n ( u s u a l ly ) t h e s i tu a t io n d e s c r i b e d in f r a m e - s t a t e m e n t 2 a l s o h o l d s

a t t i m e T .

A n o t h e r w a y t o t h in k o f t h e re l a ti o n b e t w e e n f r a m e - s t a t e m e n t s 1 a n d 2 i s t o

c o n s i d e r t h e m t w o d i f f e r e n t v i e w p o i n t s ( i n t h e s e n s e u s e d b y B o b r o w a n d W i n o -

g r a d ( 1 9 7 7 ) ) f o r th e s a m e s i tu a t io n . S o , t o ta k e o n e o f th e e a r l ie r e x a m p l e s ,

b r i n g i n g a b r u s h i n t o c o n t a c t w i t h a n o b j e c t c a n b e s e e n f r o m a n o t h e r v i e w p o i n t

a s b r i ng i ng t he pa i n t on t he b r u s h i n t o c on t a c t w i t h t he ob j e c t . L ooke d a t i n t h i s

l i g h t , t h e i n t e r m e d i a r i e s a r e t r a n s l a t o r s b e t w e e n v i e w p o i n t s . ( T h i s i s , h o w e v e r ,

on y

a n a n a l o g y si n c e B o b r o w a n d W i n o g r a d s u s e o f v i e w p o i n t s d i f f e r in m a n y

w a y s f ro m m y use o f L E A D S - T O a n d C O M E S - F R O M . ) N a tu r al ly , vi ew p o i nt s

c a n b e m o r e o r l e s s s i m i l a r , a n d t h i s w o u l d b e a c c o u n t e d f o r b y i n t e r m e d i a r i e s

w t ri ch m a k e m o r e o r le s s r a d ic a l t r a n s la t io n s . F o r e x a m p l e , s o m e i n t e r m e d i a r i e s ,

l ik e th e G R E A T E R r e la t io n w e l o o k e d a t e a r l ie r , h a v e th e. s t a tu s o f l o g i c a l

r e l a t ions , a nd in s uc h a c a s e t he tw o f r a m e s t a t e m e n t s a r e e v i d e n t l y j u s t d i f f e r e n t

w o r d s f o r es s e n t ia l l y t h e s a m e t h i n g . B u t in o t h e r c a s e s , a s w i t h o u r ru l e o f

S T I C K Y - O N , w e s e e m t o b e a t t he b o r d e r li ne b e t w e e n a ru l e o f lo g i c an d t h e

p h y s i c a l l a w s o f o u r w o r l d . I n st il l o t h e r c a s e s w e h a v e c l e a r p h y s i c a l o r c h e m i c a l

l a w s re la ti n g o u r tw o f r a m e s t a te m e n t s . F o r e x a m p l e , o n e s u c h l a w is P R E S S


18/40

372 EUGENE CHARNIAK

w hi c h e x p l a i n s how p r e s s i ng a l i qu i d - s a t u r a te d s o l id w i l l c a us e a n i nc r e a s e i n t he

a m oun t o f l i qu i d on t he s u r f a c e o f t he s o l i d . ( I t goe s p r a c t i c a l l y w i t hou t s a y i ng

th a t w h e n I t al k o f a p h y s i c a l l a w h e r e I m e a n a c o m m o n s e n s e p h y s i ca l

l a w . ) T h e r u le o f P R E S S is u s e d in R E M - L I Q w h e r e i t r e l a te s in c r e a s in g

p r e s s u r e on t he s o l i d t o t he c ha nge o f vo l um e o f a bs o r be d l i qu i d . T ha t i s , w e

w ou l d ha ve :

R E M - L I Q - G O A L ( C H A N G E L I Q - V O L a m o u nt ' N E G A T I V E )

C O M E S - F R O M : ( . . . P R E S S 5 P R E S S 4 . . . R E M - L I Q 6 )

w h e r e R E M - L I Q 6 is t he o r d e r t o u p t h e p r e s s u re o n t h e so l id . T h e i n t e rm e d i a t e s

i n t h i s c a s e , i nc l ud i ng P RE S S , r e l a t e t w o d i f f e r e n t v i e w po i n t s . O n one ha nd w e

ha ve a n i nc r e a s e i n f o r c e , on t he o t he r w e ha ve a de c r e a s e i n vo l um e . I t i s t he

pu r pos e o f t he i n t e r m e d i a r i e s t o e xp l a i n how s uc h d i s pa r a t e t h i ngs a r e r e a l l y t he

s a m e .

2. H O W T O P U T T H E F R A M E S T O G E T H E R

T h e f i rs t s e c ti on o f t h i s pa p e r in t r oduc e d , i n a s om e w ha t i m pr e s s i on i s t i c

f a s h i on , m a ny o f t he ba s i c c onc e p t s w h i c h u nde r l i e t he r e p r e s e n t a t i on . I n t h i s ,

t he s e c ond s e c t i on , w e w i l l e s s e n t i a l l y s t a r t a t t he be g i nn i ng a ga i n , a nd pe r f o r m

e a c h s t e p i n a m or e m e t hod i c a l m a nne r . T he d i s c us s i on w i l l s t i l l f a l l s ho r t o f a

f o r m a l de s c r i p t i on , h ow e ve r , a nd f o r thos e w ho f e e l t he l a c k , a c on t e x t f r e e

g r a m m a r i s p r o v i d e d i n t h e a p p e n d i x . T o m a k e i t e a s i e r t o s e e t h e c o r r e s p o n -

de nc e be t w e e n t he r u l e s the r e a nd t he d i s c us s ion he r e , I w i l l oc c a s i ona l l y i nc l ude

r e f e re n c e s ( e . g . , / l / ) t o t h e c o r r e s p o n d i n g r u l e n u m b e r . A p r o g r a m w h i c h i n c o r -

po r a t e s the s e r u l e s ha s be e n w r i t te n a nd u s e d t o c he c k a l l o f t he f r a m e s t o e ns u r e

t ha t t he y f o l l ow t he i nd i c a t e d f o r m a l i s m .

2 1 Fram es and Frame Types

S i nc e e ve r y t h i ng t he r e p r e s e n t a t i on c a n e xp r e s s i s t o be f ound i n one f r a m e o r

a no t he r , t he d i v i s ion i n to t ype s o f f r a m e s c o r r e s pon ds t o t he v i e w o f t he w or l d

a s s um e d by t he r e p r e s e n t a t i on . A t t he h i ghe s t l e ve l t he r e i s t he u s ua l d i v i s i on

be t w e e n a c t i ons a nd s t a t e s , a nd e a c h o f t he s e c om e s i n t w o va r i e t i e s , g i v i ng u s

f o u r b a s i c k i n d s o f f r a m e s : c o m p l e x e v e n t , s i m p l e e v e n t , s t a t e , a n d o b j e c t .

( T h e r e i s a f if th k in d , t h e a d ju n c t f r a m e , w h i c h w e w i ll d e s c ri b e l a t e r . ) / 2 / A s w e

s ha l l s e e , t he f r a m e t ype de t e r m i ne s t o a l a r ge e x t e n t w ha t m a ke s up t he f r a m e .

Simple Event T h e d i s t i n c t i o n b e t w e e n c o m p l e x a n d s i m p l e e v e n t s i s t h e

d is ti nc ti on b e t w e e n P A I N T I N G a n d th e c o m m o n s e n s e ca u s al l aw s o n w h i c h it

d e p e n d s . E a c h s i m p l e e v e n t f r a m e d e s c r i b e s a s i n g l e c a u s e a n d e f f e c t r e l a ti o n ,

w h e r e a s c o m p l e x e v e n t f r a m e s a r e h e l d t o g e t h e r n o t b y c a u s a l r e l a t i o n s , b u t

r a t he r by t i m e r e l a t i ons , i . e . , a t yp i c a l c om pl e x e ve n t ha s t he f o r m , f i r s t you do

t h is , a n d t h e n y o u d o t h a t, a n d . . . . C o m p l e x e v e n t s n e v e r c o n t a in c a u s al

r e l a t i ons be c a us e t he r e i s no ne e d f o r s uc h r e l a t i ons . P r e s um a b l y i f c e r t a i n


19/40

A F R A M E D P A I N T I N G 3 7,3

a c t i ons i n a c om pl e x e ve n t l e a d t o a c e r t a i n r e s u l t ( by a c a us a l r e l a t i on ) t h i s w i l l

b e a s th e r e su l t o f s o m e c o m m o n s e n s e p h y s i c a l l a w w h i c h w i ll b e e x p r e s s e d a s a

s i m p l e e v e n t . R a t h e r t h a n e x p l i c i t l y i n c l u d e t h e c a u s a l r e l a t i o n i n t h e c o m p l e x

e v e n t f r a m e ( w h i c h a s w e h a v e s e e n w i l l i n m o s t c a s e s l e a d t o u n n e c e s s a r y

d u p l ic a ti o n o f i n f o rm a t i o n ) w e c a n i n st e ad i n cl u d e a L E A D S - T O p o i n t e r in th e

c o m p l e x e v e n t p o i n t i n g t o t h e s i m p l e e v e n t .

N o w t h e a b o v e d e s c r ip t i o n te n dS t o m a k e i t s o u n d a s i f t h e r e p r e s e n t a ti o n h a s

b u i l t i n t o i t a p h y s i c i s t ' s v i e w o f a d e t e r m i n i s t i c w o r l d w h i c h r u n s a c c o r d i n g t o

f i xe d c a us a l l a w s . I n f a c t , t h i s i s no t t he c a s e . F o r one t h i ng , t he l a w s e xp r e s s e d

in th e s i m p l e e v e n t s m a y o n l y s o m e t i m e s a p p l y ( in w h i c h c a s e t h e r e w i ll b e a

" S O M E T I M E S " m a r k e r b y t he c a u se s t a te m e n t / 4 / ) , a n d fo r a n o th e r , t h er e a re

n o p a r t i c u l a r r e s tr i c ti o n s o n t h e k i n d o f c a u s a l r e l a ti o n s w h i c h m a y b e e x p r e s s e d .

S o , f o r e x a m p l e , a c h i l d ' s u n d e r s t a n d i n g o f th e w o r k i n g s o f an e le c t r ic l i g h t

m i g h t b e e x p r e s s e d a s a " c a u s a l " l aw o f th e f o r m " t h e s w i tc h i n t he o n ( o f f)

p o s i t i o n c a u s e s t h e l i g h t b u l b t o g i v e ( n o t g i v e ) l i g h t . " O r f o r t h a t m a t t e r o n e

c o u l d i n c l u d e a " l a w " w h i c h c l a i m s th a t k i s si n g a f r o g s o m e t i m e s c a u s e s i t t o

c ha nge i n t o a p r i nc e .

W e h a v e a l re a d y s e e n o n e e x a m p l e o f a s i m p l e e v e n t , n a m e l y , S T I C K in F i g.

4 , a n d w e h a v e a n o t h e r b e l o w i n F i g . 1 1 . ( I n F i g . 1 , a n d h e n c e f o r t h , a " ; "

i n d i c a te s t h a t th e r e s t o f t h e li n e i s c o m m e n t , a n d n o t p a r t o f t he f r a m e . ) B e s i d e s

t h o s e f e a t u r e s w h i c h a ll f r a m e s s h a r e ( i . e ., a n a m e , f r a m e ty p e i n d i c a t o r , a n d

v a r ia b l e l i s t / t / ) o u r s im p l e e v e n t s a ls o h a v e a s e c ti o n h e a d e d E V E N T w h i c h

d e s c ri b e s w h a t h a p p e n s . A s m e n t i o n e d a b o v e , a s i m p l e e v e n t a l w a y s c o n s is t s o f

a s i ng l e c a us a l r e l a t i on i n w h i c h t he be f o r e a nd a f t e r s e c t i ons c ons i s t o f a s i ng l e

f o r m u l a / 3 / . ( N o t e m y us e h e re o f " f o r m u l a " a s c o n tr a st ed w i th " s t a t e m e n t . "

A s I w il l u s e th e t e r m s h e r e , a s t a te m e n t c o n s i s t s o f a si n g l e p r e d i c a t e - a r g u m e n t

s t ru c t u r e , p lu s n a m e , p l u s t a g s. A " f o r m u l a " m a y s i m p l y b e a s t a t e m e n t , b u t it

m a y a l s o b e s e v e r a l s t a t e m e n t s c o n n e c t e d t o g e t h e r b y t h e l i k e s o f A N D , O R ,

e t c . )

D I R T Y - O B J E C T ( S I M P L E - E V E N T )

VA RS : ; Th is section specifies the variables.

; The actual format will be given in

; Section 3.3.

E V E N T : [ -- D I R T Y - O B J E C T I

| ( A N D D I R T Y -O B J E C T 2 ( P A I N T - C O A T P A I N T O BJ S U R F A C E )

| ; a P A I N T - C O A T o n th e S U R F A C E o f O B J

| D I R T Y - O B J E C T 3 ( D I R T Y S U R F A C E ) )

/ C A U S E S ( S O M E T I M E S )

/ ( B E F O R E ( B E G IN D I R T Y - O B J E C T I) ( B E G IN D I R T Y -O B J E C T4 )

| (1 YE AR ) )

t - D IR T Y - O B J 4 ( O R D I R T Y - O B J E C T 5 ( C R A C K P A I N T ))

D I R T Y - O B J E C T 6 ( F L A K E P A I N T ) )

FIG. I I The s imple even t DIR TY -OB JEC T.


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3 7 4

EUGENE CH RNI K

N o r m a l l y i t is a s s u m e d t h at s i m p l e e v e n t s h a p p e n v i r tu a l ly i n s t a n t a n e o u s l y a s

is t he c as e f o r S T I C K . B u t th is is n o t tr u e f o r D I R T Y - O B J E C T , w h i c h is

i n t e nde d t o e xp r e s s t he f a c t t ha t i f one h a s a c oa t o f pa i n t ove r a s u r f a c e w h i c h i s

d i r ty , t he pa i n t i s l i ke l y t o c r a c k o r f l a ke . T h a t t he c r a c k i ng o r f l a k i ng t a ke s a bo u t

a y e a r t o o cc u r is e x p r e ss e d in th e e v e n t b y t h e ti m e re la ti o n. ( B E F O R E ( B E G I N

D I R T Y - O B J E C T I ) ( B E G I N D I R T Y - O B J E C T 4 ) ' (1 Y E A R ) ) . ( T h e o n e y ea r,

a s w i t h a ll num be r s u s e d in t he f r a m e s , h i de s an i m p l i c i t a l t h ou gh t h is c a n va r y

b y a f a ct o r o f f o u r . )

O t h er a ll o w ab l e t im e re la ti on s in c lu d e D U R I N G a n d S A M E - T I M E , a n d

na t u r a l l y e nough one c a n t a l k a bou t t he e nd i ng t i m e o f s t a t e s a nd a c t i ons a s w e l l

a s t h e b e g i n n i n g / 5 / / 6 / / 7 / .

Co m p l ex E ven t s

A s f o r c o m p l e x e v e n t s , t h e y d e s c r i b e a n e v e n t i n t e r m s o f a

c o l le c t io n o f f o r m u l a s w i th t i m e r e l a ti o n s i n te r r el a ti n g t h e f o r m u l a s / 1 0 / . C o m -

p l e x e v e n t s a l s o h a v e a s e c t i o n w h i c h s i m p l e e v e n t s d o n o t , n a m e l y , G O A L ,

w h i c h de s c r i be s t he no r m a l l y de s i r e d r e s u l t i ng s t a t e o f t he e ve n t

[8[

M a n y

c o m p l e x e v e n t s , h o w e v e r , d o n o t h a v e a g o a l i n t h i s s e n s e , a t y p i c a l o n e b e i n g

t e nn i s , w h i c h i s u s ua l l y done f o r i t s ow n s a ke . I n s uc h c a s e s t he goa l w i l l be

m a r k e d in s te ad w it h t he sp e c ia l f r a m e O W N - R E W A R D . F o r g o a l - d ir e c te d a c -

t iv it ie s t he G O A L w i ll a lw a y s h a v e a C O M E S - F R O M p o i n te r in to th e e v e n t.

T h i s s e rv e s to d e s cr i b e h o w t h e e v e n t p r o d u c e s t h e d e s i re d g o a l / 9 / . F o r e x a m p l e ,

i n P A I N T I N G w e w i l l h a v e t o i n c l u d e a p o i n t e r f r o m t h e g o a l s t a t e t o P A I N T -

I N G 22 ( b r i ng i n s t r um e n t i n c o~ t a c t w i t h ob j e c t ) . T he i n t e r m e d i a r i e s on t h i s

C O M E S - F R O M p o i n t e r w i ll in e f fe c t s ta te h o w i t i s t h at b r i n g i n g t h e b r u s h i n to

c on t a c t w i t h t he ob j e c t s e r ve s t o c oa t t he ob j e c t w i t h pa i n t .

Sta tes A s t a t e f r a m e de s c r i be s a s t a t e m uc h a s a n e ve n t f r a m e de s c r i be s a n

e ve n t . N a t u r a l l y t he r e i s no a c t i v i t y i nvo l ve d , bu t a s w e no t e d i n S e c t i on 1 . 4 ,

t he r e ar e va r i ous r e la t i ons be t w e e n t he g i ve n s ta t e a nd o t he r s . S o , f o r e xa m pl e ,

w e p o i n t e d o u t i n S e c t i o n 1 . 4 h o w S T I C K Y - O N r e l a t e d t o o t h e r s t a t e s l i k e

S U P P O R T ( A st ic k y -o n B ~ B su p p or t A ) a nd E X T E R I O R ( A st ic k y - o n B

A i s on t he e x t e r i o r o f B ) . A t t he m om e n t a l l r e l a t i ons a r e o f t he f o r m A

I M P L I E S B , o r A I F F B ( I F a n d o n l y I F ) , a l t h o u g h i t m a y h a v e a m o d i f i c a t i o n

s u c h a s s o m e t i m e s a t ta c h e d to in d i c at e t h at t h e r u le m a y fa i l t o h o l d / 1 2 / / 1 3 / .

T h e s e r e l a t i o n s a r e g a t h e r e d t o g e t h e r u n d e r t h e h e a d i n g R E L A T I O N S a n d

c ons t i tu t e the bu l k o f m os t s ta t e f r a m e s ( se e F i g . 12). T he r e a r e , how e v e r ,

b e si de s R E L A T I O N S , t w o o p ti on a l p o rt io n s to s ta te f r am e s , C O M E S - F R O M

a n d L E A D S - T O / 1 1 / . T h e s e h a v e m u c h t he s am e p u rp o s e h er e a s t h ey d o i n

t h e ir m o r e f a m i l ia r r o le a s a d d i ti o n s t o f r a m e s t a t em e n t s . F o r e x a m p l e , t h e

C O M E S - F R O M ta g in th e S T I C K Y - O N f r a m e po in ts to th e n o r m a l m e t h o d fo r

a c h ie v in g S T I C K Y - O N , n a m e l y , th e ru l e o f S T I C K ( se e n i n S e c ti o n 1 .2 ).

L E A D S - T O g i v e s c o m m o n r e s u lt s, o r u s e s , o f t he s ta te . T o t a k e a n o t h e r c a s e ,

A B S O R B E D - B Y ( F ig . 13 ) L E A D S - T O p o i n ts t o t he r u le o f p r e ss u r e c a u s in g

m or e l i qu i d t o c om e t o t he s u r f a c e .


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A F R A M E D P A I N T IN G 3 7 5

ABSORB ED-BY (STATE)

RELATIONS: vAB SOR BED -BYI (ABSORBED-BY FLU SOL)

LI MPLIES

ABSORBED-BY2 (SUPPO RT SO L FLU)

ABSORBED-BY3 (ABSORBED-BY FLU SOL)

MPLIES

BSORBED-BY4 (STICKY-ON SUR FLU SOL-SUR)

COM ES-FROM : ABSO RPTION 5 ; th is describes how a l iquid which

; is sticking to an absorbant object

; w il l come to be absorbed by i t

LEAD S-TO: PRESS2 ; desc ribes he previously mentioned

; ru le of pressure

VO L-C HA NG E2 ; describes how adding or subtract-

; ing from total absorbed fluid

; w il l also change the volume on

; surface

FIG. 12 The ABSO RBED -BY frame.

Objects A s f o r o b j e c t f ra m e s , s u c h a s t h o s e d e s c r i b i n g p a i n t b r u s h e s , r o l le r s ,

e t c . , I w i l l h a v e l i tt le t o s a y a b o u t t h e m . T h e y a r e m o s t s i m i l a r t o s ta t e f r a m e s ,

b u t t h e r e la t io n s p o rt io n is r e p l a c e d b y a D E S C R I P T I O N p o r t io n w h i c h , n a

Framed Painting

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