utterance production computational model

7/29/2019 Utterance Production Computational Model

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A C o m p u t a t i o n a l M o d e l o f I n c r e m e n t a lU t t e r a n c e P r o d u c t i o n i n T a s k - O r i e n t e d D i a l o g u e s

K o h j i D o h s a k aN T T B as ic R esea rch L abora to r i e s

3 -1 Mor inosa to -w akam iya ,A t sug i , K anagaw a , 243-01 Japand o h s a k a @ a t o m. b r l . ntt. j p

A k i r a S h i m a z uN T T B as ic R esea rch L abora to r i e s

3-1 Morinosato-wakamiya,Atsugi , Kanagawa, 243-01 Japans hima z u@a t om. b r l . n t t . j p

A b s t r a c tT h i s p a p e r p r e s e n t s a c o m t m t a t i o n a lm o d e l o f i n c r e m e n t a l u t t e r a n c e p r o d u c -t i o n i n t a s k - o r i e n t e d d ia l o g u e s . T h i sm o d e l i n c r e m e n t a l l y p r o d u c e s u t t e r -a n t e s t o p r o p o s e t h e s o l u t io n o f a g i v e np r o b l e m , w h i le s i m u l t a n e o u s l y s o l v i n gt h e p r o b l e m i n a s t e p w i s e m a n n e r . E v e nw h e n t h e s o l u t i o n h a s b e e n p a r t i a l l y d e -t e r m i n e d , t h i s m o d e l s t a r t s u t t e r a n c e st o s a t i s f y t i m e c o n s t r a i n t s w h e r e p a u s e si n m i d - u t t e r a n c e m u s t n o t e x c e e d a c e r -t a i n l e n g t h . T h e r e s u l ts o f a n a n a l y s i so f d i s c o u r s e s t r u c t u r e i n a d i a l o g u e c o r -p u s a r e p r e s e n t e d a n d t h e f in e s t r u c t u r eo f d i s c o u r s e t h a t c o n t r i b u t e s t o t h e in -c r e m e n t a l s t r a t e g y o f u t t e r a n c e p r o d u c -t i o n i s d e s c r i b e d . T h i s m o d e l u t i l iz e ss u c h a d i s c o u r s e s t r u c t u r e t o i n c r e m e n -t a l l y p r o d u c e u t t e r a n c e s c o n s t i t u t i n g ad i s c o u rs e . P r a g m a t i c c o n s t r a i n t s a r e e x -p l o i t e d t o g u a r a n t e e t h e r e l e v a n c e o f di s-c o u r s e s , w h ic h a r e e v a l u a t e d b y a n u t t e r -a n c e s i m u l a t i o n e x p e r i m e n t .

1 I n t r o d u c t i o nD i a l o g u e s o c c u r i n r e a l - t i m e a n d s o a r e s u s c e p -t i b l e t o t i m e c o n s t r a i n t s . F o r e x a m p l e , d i a l o g u ep a r t i c i p a n t s m u s t p r o d u c e u t t e r a n c e s u n d e r t i m ec o n s t r a i n ts w h e r e p a u s e s i n m i d - u t t e r a n c e m u s tn o t e x c e e d a c e r t a i n l e n g t h . M o r e o v e r , p a r t i c i -p a n t s a r e i n f e r e n c e - l i m i t e d ( W a l k e r a n d R a i n b o w1 9 9 4 ) . D u e t o t i m e c o n s t r a i n t s a n d l i m i t s in i l ff e r -e n c e , d i a l o g u e p a r t i c i p a n t s c a n n o t h e l p p r o d u c i n gu t t e r a n c e s i nc r e m e n t a ll y . I n c r e m e n t a l u t t e r a n c ep r o d u c t i o n i s c h a r a c t e r i z e d l ik e t h is : s p e a k e r s p r o -d u c e u t t e r a n c e s w h i l e d e l i b e r a t i n g w h a t t o sa y~a n d r e f i n e w h a t t h e y w i l l s a y w h i l e a r t i c u l a t i n gt h e f i r st p a r t o f t h e i r u t t e r a n c e s .

T h e i n c r e m e n t a l s t r a t e g y o f u t t e r a n c e p r o d u c -t i o n p l a y s a c r u c i a l r o l e i n s p o k e n d i a l o g u e s i n t w or e s p e c t s . F i r s t , i t h e lp s s p e a k e r s t o s a t i s f y t i m ec o n s t r a i n t s o n p a u s e s . T h i s i s c r u c i a l si n c e l e n g t h yp a u s e s i m p l y t h e t r a n s i t i o n o f a t u r n f r o m t h e c u r -

r e n t s p e a k e r t o o t h e r s . S e c o n d , i t h e lp s h e a r e r s t oe a s i l y u n d e r s t a n d u t t e r a n c e s s i n c e i t e n a b l e s t h ep i e c e m e a l t r a n s m i s s i o n o f i n f o r m a t i o n .

T h i s p a p e r p r e s e n t s a c o m p u t a t i o n a l m o d e l o fi n c r e m e n t a l u t t e r a n c e p r o d u c t i o n i n t a s k - o r i e n t e dd i a l o g u es . T h i s m o d e l p r o d u c e s u t t e r a n c e s t o p r o-p o s e t h e s o l u t io n o f a g i v e n p r o b l e m w h i le s i m u l t a -n e o u s l y s o l v in g t h e p r o b l e m i n a s te p w i s e m a n n e r .T o s a t i s fy t i m e c o n s t r a i n t s o n p a u s e s , t h is m o d e ls t a r t s u t t e r a n c e s e v e n w h e n t h e s o l u t io n h a s n o tb e e n f u l l y d e t e r m i n e d a n d r e f i n e s o n t h e s o l u t i o nd u r i n g t h e a r t i c u l a t i o n o f u t t e r a n c e s .

W e p r e s e n t t h e r e s u l ts o f a n a n a l y s i s o f d i s-c o u r s e s t r u c t u r e i n a c o r p u s o f J a p a n e s e t a s k -o r i e n t e d d i a l o g u e s a n d s h o w t h a t t h e f in e s t r u c -t u r e o f d i s c o u r s e p r e v a i l s in s p o k e n d i a l o g ue s a n dt h e p r e d o m i n a n t d i s c o u r s e s t r u c t u r e c o n t r i b u t e st o t h e i n c r e m e n t M s t r a t e g y . B a s e d o n s u c h a d i s-c o u r s e s t r u c t u r e , t h is m o d e l i n c r e m e n t a l l y p r o -d u c e s u t t e r a n c e s c o n s t i t u t i n g a d i s c o u rs e . H o w -e v e r , t h e i n c r e m e n t a l s t r a t e g y i s s u b j e c t t o g e n -e r a t i n g ir r e l e v a n t d i s c o u rs e s . T o g u a r a n t e e t h er e l e v a n c e o f d i s c o u r s e s , t h i s m o d e l u t i li z e s p r a g -m a t i c c o n s t r a i n t s a n d a c o n t e x t m o d e l , w h i c h a r ee v a l u a t e d i n a n u t t e r a n c e s i m u l a t i o n e x p e r i m e n t .2 R e l a t e d R e s e a r c hR e c e n t s t u d i e s o f h u m a n s p e e c h p r o d u c t i o n ( L e v -e l t 1 98 9 ) s h o w t h a t h u m a n s p e a k e r s f r e q ue t a tl yu s e th e i n c r e m e n t a l s t r a t e g y o f u tt e r a n c e p r o d u c -t i on . T h i s p a p e r i s c o n c e r n e d w i t h a c o m p u t a -t i o n a l m o d e l o f i n c r e m e n t a l u t t e r a n c e p r o d u c t i o n .

C o m p u t a t i o n a l m o d e l s f or t h e i n c r e m e n t a ls y n t a c t i c f o r m u l a t i o n o f a s e n t e n c e w e r e p r o -p o s e d ( K e m p e n a n d H o e n K a m p 19 87 ; D e S m e d ta n d K e m p e n 1 9 91 ). A l t h o u g h i n c r e m e n t a l s y n ta c -t ic f o r m u l a t i o n i s a n i m p o r t a n t i s su e , w e d o n o ta d d r e s s t h i s h e r e .

P O P E L i s a p a ra l le l a n d i n c r e m e n t a l n a t -u r a l l a n g u a g e g e n e r a t i o n s y s t e m ( F i n k l e r a n dS c h a u d e r 1 9 92 ; R e i t h i n g e r 1 9 9 2 ). I n P O P E L , t h e" w h a t t o s a y " c o m p o n e n t d e t e r m i n e s t h e c o n t e n tt o b e g e n e r a t e d a n d g r a d u a l l y c a r r i e s i t o v e r tot h e " h o w t o s a y " c o m p o n e n t , w h i c h f o r m u l a t e s as e n t e n c e i n c re m e n t a ll y . P O P E L c a n g e n e r a t e di s-

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(1 .) a i ko - is h i d a m a d e d e s u n e / (2 ) i t t e / < h a i >P N t o C O l 'U L A g o( t o T h e i i k o - i s h i d a s t a t i o n ) ( g o)

( 3 ) s ok ode ba s u na nde s uga / ~ tot h e n b u s COI'ULA FIId,I,;I((then b.s) (ullm)

(d ) m o r i no s a t o - a o y a m a - i k i t o i u < ha l > ba s u g aP N n a m e t I b t l s S u I I .Ia m - n o d e /e x i s t - C A U S A l ,

( a s t h e r e i s a I r e s i t a m e d m o r i n o s a t o - a o y a m a - i k i )( 5 ) s o re n i no t t e - m o r a t t e / < ha l >

i t O B J gc ' t on( g e t () i t i t )

( N o t e : < h a l > s h o w s t h a t t h e d i a lo g u e p a r t n e r in -s e r t s a n u t t e r a n c e t o p r o v i d e a c k n o w l e d g n m n t . )

F i g u r e 1 : P a r t o f t r a n s c r i p t i o n o f d i a l o g u ec o u r s e s u s i n g e o n t e x t u M i n f o r m a t i o n , t l o w e v e r ,i t d ( l es n o t a l l o w f o r t h e l i n e s t r u c t u r e ( )f d i s -c o u r s e p r e v a i l i n g i n s t ) o k e n d i M o g u e s . W e l ) r e s e n ta e o m l m t a t i o n a l m o d e l o f i n c r e m e n t a l u t t e r a n c el ) r o d u e t i o n u s i n g t h e l i n e s t r u c t u r e o f d i s c o u r s e.

C a r l e t t a , C a l e y , a n d I s a r d ( 1 9 9 3 ) p r o i) o s e d a na r c h i t e c t u r e f o r t i m e - c o n s t r a i n e d l a .n g u a g e p r o -d u c t i o n . A s f o r p h e n o m e n a p e c u l i a r t o st ) o k en d i-a lo g u e s , t h e y fo c u s e d o n t l e s i l ; L t io n a n ( l s e l f - t e l ) a i r .A l t h o u g h o u r m o d e l c a , n 1 ) r o d u c e f i l l e r t e r m s a n dr e p a i r p r i o r u t t e r a n c e s , o u r c h i e f c o n c e r n i s t h et i n e s t r u c t u r e o f s p o k e n d i s c o u r s e, w h i c h i s cl o s e l yr e l a t e d t o i n c r e m e n t a l u t t e r a n c e p r o ( t n c t i o n .3 D i s c o u r s e S t r u c t u r e A n a l y s i sW e a n a l y z e d t h e d i s c o u r s e s t r u c t u r e i n a c o r p u so f t a s k - o r i e n t e d d i a h ) g u es , w h i c h w e r e c o l l e ct e d b yt h e fo l h) w i ng m e t h o d . T h e s u b j e c t s w e re n i n e t yn a t i v e J a p a i m s e . I n e a c h d ia h ) g u e , t w o s u b j e c t s ,N a n d E , w e r e ~ Ls ke d t o c o n v e r s e b y t e l e p h o n et o l i nd a s o l u t i o n t o t h e l ) r o b l e m o f h o w N c o u l dg e t f r o m o n e p l a c e t o a n o t h e r . S u b j e c t s w e r e c h o -s e n s u c h t h a t E h a d e n o u g h k n o w l e d g e t o s o l v et h e p r o b l e m b u t N d i d n o t . E i g i l t y d i a l o g u e sw e r e r e c o r d e d a n d t r a n s c r i b e d . F i f t e e n d i a l o g u e sw e r e r a n d o m l y c h o s e n f o r a n a l y s i s. T h e d i s c o u r s es t r u c t u r e w a s a n a l y z e d i n t e rm s o f i n f o r m a t i o nu n i t s a n d d i s c o u r s e r e l a t i o n s .a . 1 A n a l y z i n g i n f o r m a t i o n u n i t sS p e a k e r s o r g a n i z e t i le i n f o r m a t i o n t o t )e c o n v e y e dt o i n f o r m a t i o n u n i t s ( H a l l i d a y 1 9 9 4 ), w h i c h a ret h e u n i t s f o r t r a i t s m i s s i o n o f i n f o r m a t i o n . T h e i n -f o r m a t i o n u n i t s ( I K s f o r s h o r t ) a r e r e g a r d e d a sminilnal components of d i s c o u r s e s t r u c t u r e . W ea s s u m e t h a t I U s a,re r e a l iz e d b y g r a m m a t i c a l l ie -v i c e s : a c l a u s e r e a l i z e s a n 1 U , a n i n t e l j e c t o r y w o r dr e a l i ze s a n 1U, a n d a t il le r t e r m s h o w s t h e e n d o fan IU. F i g u r e 1 s h o w s p a .r t o f t h e t r a n s c r i p t i o n o fa d i a l o g u e w h e r e a d i a h l g u e p a r t i c i p a n t p r o l )o s e sa d o m M n l ) la n . T i l e s y m b o l " / " s e p a r a t e s t h e IUs.

T a b l e 1 : F r e q u e n c y d i s tr i b u t io n f o r i n f o r m a t i o n u n i t sC l a u s e 9 2 9I n t e r j e c t o r y w o r d 6 6 5P P o r N P 2 79C o n j u n ( : t i o n 8 4S e q u e n c e o f P P s o r N P s 4 1O t h e r s 1 4T o t a l 2 0 1 2

T a l ) le 1 s h o w s t h e f r e q u e n c y d i s t r i b u t i o n f o r t i m/~ r a m n la t i e a ] ( : a t e g o r i c 's o f IU, w h e r e N P a n d I ' Pm e a n n o u n 1 ) h ra s e a n d 1 ) o s t l )o s i t io n a l p h r a s e . ' .[ 'h ea v e r ag e n m n b e r o f N P s i n a n IU a s a c l a u s e , N P ,P l ' , o r s e q u en ( - e o f N P s a n d P l ? s i s 1 .0 1 i n t h et i f t e e n d i a l o g u e s . T h e v m ' i a n e e is 0 . 2 8 .

T h i s r e s l f l t i n d i c a t e s t h a t s m a l l IUs a r e f r e -q u e n t l y u s e d . F o r e x a m p l e , a l t h o u g i l IU (1) inF i g u r e 1 d e s cr i l) e s o n l y a p a r t o f a d o m a i n a c -t i o n , i t i s r e g a r d e d a s a i l IU s i i l . ce i t has a e ( /pu la( " d e s u " ) a n ( 1 a s e n t e n e e - l i n a l t ) a r t i c l e ( " n e " ) .3 . 2 A n a l y z i n g d i s c o u r s e r e l a t i o n sD i s c o u r s e r e l a t i o n s b e t w e e n a d j a c e n t d i s c o u r s es e g m e n t s w ( ,. re e x a m i n e d . A ( l i s c o u r se segmenti s an IU o r a s e q u e n c e o f IUs. F o r d i s c o u r s e r e -t a .t i o ns , w e h e r e a d o t ) t e d t h o s e u s e d i n R h e t o r i -( :a l S t r u c t u r e T h e o r y ( M ~ n n a n d T h o m t ) s o n 1 98 8 )a n d t l e re f o l l o w e d H o v y ( 1 9 9 3 ) t o c l a s s i f y t h e mi n t o s e m a n t i c a n d i n t e r p e r s o n a l o n e s . F i g u r e 2s h o w s d i s c o u r s e r e l a t i o n s t l l a t a p p e a r i n t h e d i s -c o u r s e d i s p l a y e d i n F i g u r e 1 . T h e s m a l l I U s a r e h i-e r a r c h i c a l l y r e l a t e d . T h i s r e s u l t s i ll t h e f i n e s t r u c -t u r e o f d i se o m : s e.T a b l e 2 s h o w s t i l e f r e q u e n c y d i s t r i b u t i o n s f o rd i s c o u r s e r e l a t i o n s i n t i l e f i f t e en d i a k ) g u e s . L e t u sc o n s i d e r t h e r o l e t h a t t il e l ) r e d o m i n a n t r e l a ti o n s ,E l a b o r a t i o n , C i r c u m s t a n c e , a n d M o t i v a t i o n , l ) la y i nt il e i n e r e i n e n t a l s t r a t e g y o f u t t e r a n c e t ) r o d u ct i o n . *F i r s t , E l a b o r a t i o n is e x p l o i t e d t o d e s c r i b e d o m a i na c t i o n s , s t a t e s o r o b j e c t s i n a p i e c e m e a l f a s h i o n .E l a b o ra t io n e n a b l e s s p e a k e r s t o d i s t r i b u t e t h e c o n -t e n t t o b e c o n v e y e d a m o n g d i f f e r e n t l U s . '_ Pt fi s r e -l a t i o n i s u s e f ul f o r t h e i n c r e m e n t a l s t r a t e g y s i n cei t a l l o w s s p e a k e r s t o b e g i n u t t e r i n g e v e n w h e n t h ec o n t e n t h a s n o t b e e n f u l l y d e t e r m i n e d .

S e c o n d , C i r c u m s t a n c e is t h e r e l a t i o n b e t w e e nt w o s e g m e n t s , a n u c l e u s a n d a sa t e ll i t e. T h e m >e l e us d e s c r i b e s a d o m a i n a c t i o n o r s t a t e . T h es a t e l l i t e d e s c r i b e s t h e c i r c u m s t a n c e s w h e r e t h e m >c l e u s i s i n t e r p r e t e d , s u c h a s t h e p r e c o n d i t i o n s o fa d o m a i n a c t i o n . T h e r e a r e 4 1 c a s es w h e r e t h es a t e l li t e d e s c r i b e s a p r e c o n d i t i o n o f a d o m a i n a c -t i o n , w h i c h a m o u n t s t o 6 8 % o f al l c a s es . T h e c o n -s t i t u e n t s o f a d o m a i n a c t i o n a r e o f t e n r e f er r e d t oi n it s p r e c o n d i t i o n s . W e se e ~ t y p i c a l e a s e in t i ler e l a t i o n l ) e t w e e n ( 4 ) a n d ( 5 ) i n F i g u r e 1 . ( 5 ) d e -s c r i b es t h e a c t i o n o f g e t t i n g o n a b u s a n d ( 4 ) d e-

1 W e fo u n d n o d i r e c t r e h ~ tio n s hip b e tw e e n Sequenceand the increme.nt~d strategy.

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Sequence/ Ci rcumstance , Mo t iva t ion/E l a b o r a t i o n E l a b o r a t i o n(1) (2) (3) (4) (5)F i g u r e 2 : D i s c o u r s e r e la t io n s n F i g u r e 1

T a b l e 2 : D i s t ri b u t i o n fo r d is c o u r s e r e l a tio n sE l a b o r a t i o n 3 05S e q u e n c e 74C i r u c u m s t a n c e 6 0R e s u l t 2 5Co n di t i o n 2 5P u r p o s e 2C o n t r a s t 1

( a ) S e m a n t ic r e la t io n s

M o t iv a t io n [ i lB a c k g r o u n dE v i d e n c eI n t e r p r e t a t i o nC o n c e s s i o nE n a b l e m e n t( b ) I n t e r p e r s o n a lr e l a t i o n s

s c r i b e s t h e e x i s t e n t i o n a l s t a t u s o f t h e b u s m s t h ep r e c o n d i t i o n o f t h e a c t i o n . B y u t i l i z i n g th i s r e l a -t i o n , s p e a k e r s c a n d i s t r i b u t e t h e c o n t e n t o f a d o -m a i n a c t i o n b e t w e e n t w o I U s . T h e y c a n p i c k u pa c o n s t i t u e n t o f a n a c t i o n a n d d e s c r i b e i t b e f o red e s c r i b i n g t h e w h o l e c o n t e n t o f t h e a c t i o n . T h u sC i r c u m s t a n c e i s u s e f u l f o r t h e i n c r e m e n t a l s t r a t e g y .

F i n a l l y , M o t i v a ti o n is m a i n l y u s e d f o r d e s c r i b i n ga d o m a i n a c t i o n a s a n u c le u s a n d m o t i v a t i n g a d -d r e s s e e s t o a d o p t t h e a c t i o n b y p r e s e n t i n g a f a c ta s a s a t e l l i t e . I n t y p i c a l c a se s , s p e a k e r s m o t i v a t ea d d r e s s e e s t o a d o p t a n a c t i o n b y a s s e r t i n g t h a ti t s p r e c o n d i t i o n i s s a t i s f ie d . I n s u c h c a s e s , M o t i-v a t io n o c c u r s t o g e t h e r w i t h C i r c u m s t a n c e a n d c o n -t r i b u t e s t o t h e i n c re m e n ta . 1 s t r a t e g y i n t h e s a m ew a y a s C i r c u m s t a n c e .4 T h e M o d e lA s s h o w n i n F i g u r e 3 , t h i s m o d e l i s c o m p o s e d o ff iv e m o d u l e s : a p r o b l e m s o l v e r , a n u t t e r a n c e p l a n -n e r , a n u t t e r a n c e c o n t r o ll e r , a t e x t - t o - s p e e c h c o n -v e r t e r , a n d a p a u s e m o n i t o r . T h e p r o b l e m s o l v e rm a k e s d o m a i n p l a n s t h a t s o l v e a g i v e n p r o b l e m .T h e u t t e r a n c e p l a n n e r m a k e s u t t e r a n c e p l a n s top r o p o s e d o m a i n pl a n s. P r a g m a t i c c o n s t r a i n t s a n da c o n t e x t m o d e l a r e u s e d t o g e n e r a t e r e l e v a n t d i s -c o u r s e s . A c c o r d i n g t o u t t e r a n c e p l a n s , t h e u t-t e r a n c e c o n t r o l l e r s e n d s l i n g u i s t i c e x p r e s s i o n s t ot il e t e x t - t o - s p e e c h c o n v e r t e r . T h e p a u s e m o n i t o rw a t c h e s t h e l e n g t h o f p a u s e s a n d s i g na l s t h e u t t e r -a n c e p l a n n e r a n d c o n t r o l l e r w h e n t h e p a u s e l e n g t he x c e e d s a g i v e n l e n g t h .

T h e s e m o d u l e s w o r k i n p a r a ll e l . B o t h d o m a i np l a n s a n d u t t e r a n c e p l a n s a r e m a d e i n a s t e p w i s em a n n e r u s i n g t h e h i e r a r c h i c a l p l a n n i n g m e c h a -n i s m ( R u s s e l a n d N o r v i g 1 99 5 : C h a p . 1 2 ) . T h i sm o d e l s t a r t s t o m a k e a n u t t e r a n c e p l a n b e f o re af u l ly d e t e r m i n e d d o m a i n p l a n h a s b e e n o b t a i n e d .W h e n a p a u s e e x c e e d s th e t i m e l i m i t, t h e u t t e r -a n c e p l a n n e r s e n d s t h e u t t e r a n c e c o n t r o l l e r a n u t -

Inpu t: a dom ain p rob lemP a r a l le l M o d u l e s[ P r o l f l c n l S o l v c r ] [ ~ f Pragmatic ~'~k,, Cons tra intsJd o m a in p la n s ~ . . / " ]

[ - U t t e r a n c e l a n n e r ] i C o n te x t Mo d e lu t te rance l ansU t t e r a n c e C o n t r o l l e rexp ress ions

Output: utterancesF ig u re 3 : Mo de l o verv i ew

t e r e n c e p l a n o b t a i n e d w i t h i n th e t i m e l i m it . Ad o m a i n p l a n i s r e fi n e d d u r i n g t h e p l a n n i n g a n d a r -t i c u l a t o n o f u t t e r a n c e s . B a s e d o n a r e f in e d d o m a i np l a n , th e u t t e r a n c e p l a n i s r e p l a n n e d . W h e n t h eu t t e r a n c e c o n t r o l l e r i s n o t g i v e n u t t e r a n c e p l a n sw i t h i n t h e t i m e l i m i t , i t p r o d u c e s a fi l le r t e r m .5 P r a g m a t i c C o n s t r a i n t sP r a g m a t i c c o n s t r a in t s a r e r e q u ir e d t o g u a r a n t e et h e r e l e w m c e o f d i s c o u rs e s . T h i s m o d e l e x p l o i tst h e f o l l o w i n g p r a g m a t i c c o n s t r a i n t s .( c l ) A v o i d c o n v e y i n g r e d u n d a n t i n f o r m a t i o n .( (:2 ) P r o n o m i n a l i z e o b j e c t s i n t h e f o c u s o f a t t e n -t i o n ( G r o s z a n d S i d n e r 1 9 8 6 ) .( c 3) B e r e l e v a n t a c c o r d i n g t o t h e a t t e n t i o n M s t a t e .

? ['h e c o n t e x t m o d e l r e c o r d s t h e i n f o r m a t i o n t h a th a s b e e n c o n v e y e d a n d t r a c k s t h e a t t e n t i o n a ls t a t e . F o r e x a m p l e , c o n si d e r t h e d o m a i n a c t i o no f m o v i n g f r o m o n e l o c a t i o n 11 t o a n o t h e r 12. T od e s c r i b e s u c h a d o m a i n a c t i o n w i t h v e r b s s u c h a s" i k u ( g o ) " , I t m u s t b e in f o c u s . O t h e r w i s e , t h e d e -s c r i p t i o n i s i r r e l e v a n t . A f t e r s u c h a n a c t i o n h a sb e e n d e s c r i b e d , 12 i s i n th e f o c u s . M o r e o v e r , a n yo b j e c t m a r k e d a s a t o p i c b e c o m e s a f o c u s e d o n e .6 P r o b l e m S o l v i n gW e o u t l i n e t h e p r o b l e m s o l v e r u s in g a s a m p l ep r o b l e m o f h o w t o m o v e f r o m t h e M u s a s h i n o C e n -t e r t o t h e A t s u g i C e n t e r o n t h e m a p i n F i g u r e 4.T i l e p r o b l e m s o l v e r f i rs t m a k e s a n a b s t r a c t d o -m a i n p l a n , w h i c h i s a s e q u e n c e o f t h r e e a c t i o n s e l ,a2 , a n d a3 : m o v i n g fr o m t h e M u s a s h i n o C e n t e rt o t h e n e a r e s t s t a t i o n b y b us , m o v i n g to t h e s t a -t i o n n e a r e s t t h e A t s u g i C e n t e r , a n d t h e n m o v i n gt o t h e A t s u g i C e n t e r b y b u s . T h i s p l a n i s w r i t t e na s ( r l ) . T h e c o n t e n t s o f t h e s e a c t i o n s a r e w r i t t e na s ( r 2 ) . E x p r e s s i o n cont (X, Y) m e a n s t h a t t h ec o n t e n t o f X i s r e p r e s e n t e d a s a se t Y o f l i te r a ls .( r l ) p l a n ( [ e l , a 2 , a 3 ])( r2 ) c o n t ( a l , { t y p e ( e l , m o v e ) , s o u r c e ( e l , x l ) ,m a n n e r ( e l , x 2 ) , d e s t ( a l , x 3 ) } )

c o n t ( x l , { t y p e ( M , b u i l d in g ) ,n a m e d ( x l , " m u s a s h i n o s e n t a ~ " ) } )eont(x2, {type(x2, bus)})

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4/6

Musashino Center

M i t a k a K i c h i j o j i W " " ~ . . . ~ h i n j u k uj . ~ - S h i m o k i t a z a w a / x"Z o0a uL 4

Atsugi Cen terF i g u r e 4 : S a m p l e m a p

c o n t ( x 3 , { t y p e ( x 3 , s t a t i o n ) , n e a r e s t ( x 3 , x l ) } )c o n t ( a 2 , { t y p e ( a 2 , m o v e ) , s o u r c e ( a 2 , x 3 ) ,d e s t ( a 2 , x 4 ) } )c o n t ( a a , { t y p e ( a 3 , i n o v e ) , s o u r c e ( a 3 , x 4 ) ,m n.er(a3, xS), de t(a3, x6)})c o n t ( x 4 , { t y p e ( x 4 , s t a t i o n ) , n e m e s t ( x 4 , x 6 ) } )c o n t ( x 5 , { t y p e ( x 5 , b u s ) } )c o n t ( x 6 , { t y t t e ( x 6 , b u i l d i n g ) ,n a m e d ( x 6 , " a t s u g i s e n t a a " ) } )

T h e p r o b l e m s o l v er t r i es t o m a k e a m o r e c o n -c r e t e p l a n . W h e n m o r e t h a ,n o n e d o m a i n 1 ) la n i sp o s s i b l e , i t c h o o s e s t i l e d o m a i n i ) l a n t h a t r e q u i r e st h e s h o r t e s t e x e c u t i o n t i m e . I n t h i s d o m a i n , t h ed o m a i n p l a n i s a s e q u e n c e o f a c t i o n s a/t, a5, a6 a n da T: m o v i n g f r o m t h e M u s a s h i n o C e n t e r t o K i c h i-j o j i s t a t i o n b y b u s , m o v i n g t o S h i m o k i t a z a w a s t a-t i o n b y t i l e I n o k a s h i r a I A n e, m o v i n g t o A i k o - i s h i d as t a t i o n b y t h e O d a k y u L i n e , ~ md t h e n m o v i n g t ot h e A t s u g i C e n t e r b y b us . P a r t o f t h e c o n t e n t o ft h i s p l a n i s r e p r e s e n t e d a s f o l l o w s .( r3 ) phm ([a4 , a5 , a6 , a71)( r 4) c o n t ( a 4 , { t y p e ( M , m o v e ) , s o u r c e (a 4 , x l ) ,m a n n e r ( a 4 , x 2 ) , d e s t ( a 4 , x 7 ) } )

c o n t ( x T , { t y p e ( x T , s t a t i o n ) ,n a m e d ( x 7 , " k i c h i j o j i" ) } ) . .. .. .

7 U t t e r a n c e P l a n n i n gA n u t t e r a n c e p l a n i s a s e q u e nc e o f c o l n m n n i e a t i v ea c t i o n s t h a t a c h i e v e s a c o m m u n i c a t i v e g o a l. I t isr e f i n e d i n a s t e p w i s e m a n n e r . A s e q u e n c e o f s u r -f a c e c o m m u n i c a t i v e a c t i o n s c o r r e s p o n d i n g t o t h eu t t e r i n g o f l in g u i s t i c e x t ) r e s s i on s i s f i n a l l y p l a n n e d .7 . 1 C o m m u n i c a t i v e go a lsG e n e r a t i o n s y s t e m s e n g a g i n g i n d i a l o g u e s m u s tr e c o r d c o m m u n i c a t i v e g o a l s r e l a t e d t o c o m m u -n i c a t i v e a c t i o n s ( M o o r e a n d P a r i s 1 9 9 4 ). C o m -m u n i c a t i v e g o a l s u s e d h e r e a r e :

p e r s u a d e d - p l a n ( P ) : d i a l o g u e p a r t n e r i s p e r -s h a d e d t o a d o p t d o m m n p l a n P . p e r s u a d e d - a c t ( A ) : d i a l o g u e p a r t n e r i s p e r -s u a d e d t o a d o p t d o m a i n a c t i o n A .

d e sc r i b ed -even t (E , C , A t ) : d o m a i n e v e n t E i sd e s c r i b e d a s a n e v e n t h a v i n g c o n t e n t C a n ( ta t t i t u d e A t t o w a r d E i s a l s o d e s c r i b e d . d c . s c r i bed -ob j (O , 6 ) : d o m a i n o b j e c t O i s d e -s c r i b e d ~ s a n o b j e c t h a v i n g c o n t e n t C . dcscr ibcd- them.a-re l ( l?~, O, E ): t h e m a t i c r e l a -t i o n I t i s d e s c r i b e d , w h i c h d o m a i n o b j e c t Ob e a r s t o d o m a i n e v e n t E .W h e n t h e d o m a i n t ) l a n ( r l ) i s o b t a i n e d , ( r 5 ) isg i v e n a s t h e i n i t i M c o m m u n i c a t i v e g o a l .

(1 "5 ) per suadeA-p lan ( [a l , a2 , a3 ] )7 . 2 S u r f a c e c o i n m u n i c a t i v e a c t i o nsS l l r f a ( ; e c o m m n n i c a t i v ( , a c t i o n s u s e d h e r e a r e :

s v . r f acc -d e sc -c ven t (E , C , A t ) : u t t e r e x p r e s -s ions tO descr i t)e , do m ain ev en t E iLq al l even th a v i n g c o n t e n t C a n d d e s ( -r i be a t t i t u d e A t to -w a r d E . s u r face -de sc -o b j (O , C , I t ): u t t e r e x p r e s s i o n s t od e s c r i b e d o i n a i n o b j e c t O a s a n o b j e c t h a v i n gc o n t e n t C a n d b e a r i n g t h e n m t i c r e l a ti o n R t oa c e r t a i n e v e n t .

7 . 3 P l a n n i n g u t t e r a n c e s b a s e d o n t i l ef i ne s t r u c t u r e o f d i s c o u r s eA n u t t e r a n c e p b m i s e l a b o r a t e d u s i n g a c t i o ns c h e m a t a a n d d e c o m p o s i t i o n m e t h o d s . A n a c t i o ns c h e m a c o n s i s t s o f a n a c t i o n d e s c r i p t i o n , a p p l i -c a b i l i t y c o n s t r a i n t s a n d a n e f f e ( : t .2 I t de f ines ac o m m u n i c a t i v e a c t io n . A d e c o m p o s i t i o n i n e t h o( lc o n s i s t s o f a n a c t i o n d e s c r i p t i o n , a p p l i e a l ) i l it y c on -s t r a i n t s a n d a p l a n . I t s p e c if i e s h o w a n a c t i o n i sd e c o l n p o s e d t o a d e t a i l e d p h m .T h e f o l l ow i n g s c h e m a ( r6 ) d e f i n e s t h e c o m m u -n i c ; t t iv e a c t i o n o f p r o I )o s i n g a d o m a i n p l a n b y u s -i n g S e q u e nc e . T h e d e c o m p o s i t i o n m e t h o d ( rT )spec i f ies how the ~mt ion i s decomposed to a se -que nce o f f ine r ac t ions . :~(1"6) A e t ( p r o p o s e - a c t s - i n - s e q ( * P ) ,C o n s t r : p l a n ( . P ) ,E f f e c t : p e r s u a d e d - p l a n ( * P ) )( r7 ) D e c o m p ( p r o p o s e - a c t s - i n - s e q ( [ * A c t l * R e s t ] ) ,C o n s t r : * R e s t [],P l a n : [aeh i e v e (pe r su aded - ae t ( * A c t ) ) ,p r o p o s e - a c ts - i n - s c q ( * R e s t ) ]

I n t h e s e r e p r e s e n t a t i o n s , a c h i e v e ( P ) d e s i g n a t e sa n a c t i o n t h a t a c h i e v es g o a l P . N o t a t i o n [ H I L ]spec i f ies a l i s t , wh ere H i s the he ad o f the l i s t andL is t h e r e s t . S y m b o l s s t a r t i n g w i t h " * " r e p r e s e n tv a r i a b l e s . B y a p p l y i n g ( r 6 ) a n d ( r 7 ) t o t h e i n i t i a lc o m m u n i c a t i v e g o a l ( r S ), t h e f o ll o w i ng u t t e r a n c ep l a n i s o b t a i n e d :( r 8 ) a c h i e v e ( p e r s , l a d e d - a c t ( a l ) ) ,a c h i e v e ( p e r s u a d e d - a c t ( a 2 ) ) ,a c h i e v e ( p e r s u a d e d - a c t ( a 3 ) ) .

2In th is paper , we do not consider a precondit ionfo r an ac t ion schema.aWe have omi t ted o ther method to avo id in t in i ter e e u r s i v e a p p l i c a t i o n o f th e m e t h o d ( r 7 ) .

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( r9) A c t (p r opo s e - ac t @ A ) , Ef fec t : persu adcd-act ( * A ) )( r l 0 ) D ecom p(p r opo s c - ac t( *A ), C o n s t r : cont ( , A , * C ) , P l a n : achicvc( dcscr ibcd-cvcnt( , A , ,C , prop osal))( r l 1 ) A c t ( d e s c r ib c - c v c n t - b y - e la b o r a t i o n ( ,E , *C , *A t ) , Ef fec t : descr ibed-cvcnt( , E , *C, *At))( r12) D ecom p( descr ibc-event-by-elaborat ion( , E , *C , *A t), C o n s t r : *T h e m a E * C A* T h c m a = . . [ * R , * E , * 0 ] A * R t yp e A c on t( * O , , O b j C ) A * R e s t = * C - { * T h e m a }p l a n : [ ch i e( descr cd-obj( ,O , *O bjC ) ) , *R, *0 , *E ) ) ,

ac h , i e e ( d s c i ed - e e , t ( , E , , R e t , , A t ) ) ] )( r13) A c t ( de s c r i be -ob j - w i th - t hcm a( *O , *C , *R , * E ) ,Ef fec t : dcscr ibcd-obj( *O, * C ) A descr ibed- thema-rcl( ,R , * 0 , * E ) )( r14) D eco i np (dc s c r i be - ob j - w i t h - t hc r na ( ,O , * C , * R , * E ) , P l a n : s u r f ace - de s c - ob j ( ,O , *C , *R ) )( r15) A ct( dcscr ibc-cvcnt- type( ,E , * C , * A t ) , C o n s t r : * C = { t y p e ( * E , * T ) } ,Ef fec t : descr ibcd-cvcnt( , E , * C , * A t ) )( r16) De~comp ( descr ibc-event- type( , E , * C , * A t ) , P l a n : sur face-desc-event ( *E , * C , * A t ) )

Figure 5 : Ac t ion schema ta and decomposi t i on me thods fo r p ropos ing doma in ac t ion( r 8 ) i s d e c o m p o s e d b y a p p l y i n g t h e a c t i o ns c h e m a t a a n d d e c o m p o s i t i o n m e t h o d s s h o w n i nF i g u r e 5 . T h e s e s c h e m a t a d ef in e c o m m u n i c a t i v ea c t i o n s f o r p r o p o s i n g a d o m a i n a c t i o n w h i l e e l a b o -

r a t i n g t h e c o n t e n t o f t h e a c t i o n i n a s te p w i s e m a n -n e r . T h e y r e f le c t t h e r e s u l t s o f a d i s c o u r s e s t r u c -t u r e a n a l y s i s , w h i c h s h o w t h a t s p e a k e r s t e n d t od i s t r i b u t e t h e c o n s t i t u e n t s o f a d o m a i n a c t i o n i n t od i f f e r e n t IU s by using EI ,ABORATION. In ( r12) ,n o t a t i o n F ( X , 17 , . . . ) = . . [F , X , Y , . . . ] i s used fo rd e c o m p o s i n g t e r m F ( X , Y , . . . ) i n t o r e l a t i o n F a n da r g u m e n t s X , Y , . . . .W h e n d o m a i n o b j e c t s a r e l i n g u i s t i c a l ly r e a li z e db y t h e sur faee-desc-ob j i n ( r 1 4 ) , p r a g m a t i c c o n -s t r a i n t ( c 2 ) i s e x p l o i t e d t o t ) r o n o m i n a l i z e f o c u s e do b j e c t s . I n a d d i t i o n , a c c o r d i n g t o c o n s t r a i n t ( c 3 ) ,t h e o b j e c t s t h a t a r e n o t i n f o c u s n e e d t o b e t o p i -e a l iz e d i f t h e y m u s t b e i n f o c u s .B y a p p l y i n g t h e s e s c h e m a t a t o t h e f i r s t a c t i o ni n ( r 8 ) , t h e f o l l o w i n g u t t e r a n c e p l a n i s o b t a i n e d .T h e m a t i c r e l a t i o n s a r e c h o s e n i n d e f a u l t o r d e rwhen ( r12) i s app l i ed .

( r 1 7 ) s u r f a c e - d e s c -o b j ( x l , { t y p e ( x l , b u i l d i n g ) ,n a m e d ( x 1 , " m n s a s h i n o s e n t a a " ) } , s o u rc e ),s u r f a c e - d e s c - o b j ( x 2 , { t y p e ( x 2 , b u s ) } , m a n n e r ) ,s u r f a c e - d e s c - o b j ( x 3 , { t y p e ( x 3 , s t a t i o n ) ,n e a r e s t ( x a , x l ) } , d e s t ) ,s u r f a c e - d e s c - e v e n t ( a l , { t y p e ( a 1 , m o v e ) } ,p r o p o s a l ) .A c c o r d i n g t o u t t e r a n c e p l a n ( r 1 7 ) , t h i s m o d e lc a n s t a r t t h e f o l lo w i n g u t t e r a n c e s t o s a t i s f y t h et i m e c o n s t r a i n t s b e f o r e O b t a i n i n g a c o n c r e t e d o -m a i n p l a n s u c h a s ( r 3 ) .

( u l ) m u s a s h i n o s e n t a a k ar a- wa d e s u n e /P N f r o m - T o p i c C OP UL A( f r o m t h e M u s a s h i n o C e n t e r )basu de / m o ~ o r i - n o - e k i m a d e / i k i m a s u /b u s b y n e a r e s t s t a t i o n t o g o( b y b u s ) ( t o t h e n e a r e s t s t a t i o n ) ( g o )

F o r b r e v i t y , w e h a v e o m i t t e d a c t i o n s c h e m a t aa n d d e c o m p o s i t i o n m e t h o d s f o r u t t e r a n c e p l a n -n i n g u s i n g MOTIVATION and CIRCUMSTANCE.

7.4 R e p l a n n i n g u t t e r a n c e p l an sW h i l e p l a n n i n g a n d a r t i c u l a t i n g u t t e r a n c e s u s i n ga n a b s t r a c t d o m a i n p l a n , a m o r e c o n c r e t e d o m a i np l a n is b e i n g m a d e . W h e n a m o r e c o n c r e t e d o -m a i n p l a n i s o b t a i n e d , a n u t t e r a n c e p l a n i s r e -p l a n n e d . F o r e x a m p l e , c o n s i d e r t h e ca s e w h e r ea c o n c r e t e d o m a i n p l a n , ( r 3 ) , i s o b t a i n e d d u r i n gt h e p r o d u c t i o n o f u t t e r a n c e ( u l ) . T h e f o l lo w i n gu t t e r a n c e p l a n i s r e p l a n n e d :( r 18 ) s u r f a c e - d e s c - o b j ( x l , { t y p e ( x 1 , b u i l d i n g ) ,n a m e d ( M , " n m s a s h i n o s e n t a a " ) } , so u r c e) ,s u r f a c e - d e s c- o b j ( x 2 , { t y p e ( x 2 , b u s ) } , m a n n e r ) ,s u r f a c e - d e s c - o b j ( x 7 , { t y p e ( x 7 , s t a t i o n ) ,n a m e d ( x 7 , " k i c h i j o j i " ) } , d e s t ) ,su r f ace -d esc -even t ( a4 , { typ e (a4 , move ) } ,p r o p o s a l ) .

W e a s s u m e t h a t p l a n ( r 18 ) is o b t a i n e d w h e nt h i s m o d e l f i n i s h e s u t t e r i n g " m o y o ri -n o - ek i m a d e "i n u t t e r a n c e ( u l ) . T h e n ( u l ) i s i n t e r r u p t e d a n du t t e r a n c e s f o ll o w b a s e d o n ( r1 8 ) . C o n s e q u e n t l y ,t h e f o l l o w i n g u t t e r a n c e s a r e p r o d u c e d :( u 2 ) m u s a s h i n o s e n t a a k a ra - w a d e s u n e /P N f r o m - T o p l c C OP UL A( f r o m t h e M u s a s h i n o C e n t e r )

basu de / moyori-no-eki m ad e/b u s b y n e a r e s t s t a t i o n t o( b y b u s ) ( t o t h e n e a r e s t s t a t i o n )kichi joj i ma de desu ne / ikimasu /P N t o C O P U LA g o( t o K i c h i j o j i s t a t i o n ) ( g o )

I n t h e a b o v e , t h e r e d u n d a n t i n f o r m a t i o n is n o tr e s t a t e d a c c o r d i n g t o p r a g m a t i c c o n s t r a i n t @ 1 ) .Se l f - repa i r occurs : "moyor i -no-ek i mad e" i s r e -placed by "kichi joj i made".8 E x p e r i m e n t sT h i s m o d e l h a s b e e n i m p l e m e n t e d i n C o m -m o n L i s p . A lo g i c a l c o n s t r a i n t u n i f i c a t i o n s y s -t e r n ( N a k a n o 1 99 1) i s u s e d i n t h e p l a n n e r s . T h ed o m a i n p l a n n e r i n c l u d e s 1 8 a c t i o n s c h e m a t a a n d1 6 d e c o m p o s i t i o n m e t h o d s . T h e u t t e r a n c e p l a n -

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(el ) Musashino sentaa kara-wa desune /PN front-Top ic, COPULA(from the Musashino Center)

(e2) ~ t o K i c h i jo j i m a d e / d e t e - k u d a s a i /F IL I , F , I ~ PN to go-t)le~se(crm to Kichijoji station) (please go)@ 3 ) ~ to d e s u n e s o r e k a r a in o k a s hir a -s e n d eFILLER then PN by(erm then by the Inokastfira Line)(e4) odakyu-sen hi / norikaete /PN for change((:hange train for the Odakyu Line)

basu de / moyori-no-eki made /bus by nearest station to(by Ires) (to the nearest station)

desune / s h i m ok i t az aw a made /COI'UI,A PN to(to Shimokitazawa station)

aiko-ishida made / ikimasu / .....PN to go(to Aiko-ishida station) (go)

Figure 6: Discourse generated by implemented systemner includes 16 action schemata and 16 decom-position methods. We ewduated pragm atic con-straints in an utterance simulation experiment,where discourses generate.d with the constraintswere contpared with those generated withoutthem . A map inclu ding 120 h)cations such as sta-tion and 25 railr oad lines w~s used. The paus elength limit was ().5 see.When pragmatic constraints were used, this im-plemented systeIn generated relevant discourses.Figure 6 shows the discourse generated when theproblem of inoving frolIl the Mus~ksliino Center tothe Atsugi Center was given. Filler terms such asgto were produced to satisfy the time constraints.Pragmatic constraint (el) was used ill (e2), ~Uq ex-p l a i n e d in section 7.4. Con str ain t (c2) was usedto zero-proImmi nalize stati ons in the focus of at-tent ion. Con str ain t (e3) was used in ((:1) to top-icalize the Musashino Center. Topicalization wasalso used in other cases where the system mustshift the focus of atten tion to the location al-ready described in the preceding discourse. Suchcases happened when the system started utter-antes based on an abstract domain I)lan, took along time to obtain a more concrete plan, and thenelaborated on a route from a location that wasnot in focus based on the concrete plan. With-out prt~gmatic constraints, the system generatedirrelevant and excessively redundant discourses.9 C o n c l u s i o nWe presented a computatio nal model of producingutterances incrementally so as not to make exces-sively long pauses. We presented the results of ananMysis of discourse structu re and showed thatspeakers frequently use small information unitsand exploit the fine structure of discourse thatcontributes to the increlnentM production strat-egy. T his model can utilize such a discourse struc-ture to incrementally produce utterances accord-ing to pragmati c constraints. These were ewdu-ated by an utterance simulation experiment.Refe rencesCarletta, Jean; Caley, Richard; and Isard, Stephen.

i t t e /g o(go)

(1993). A system architecture for simulating time-constrained language production. Research PaperItCRC /RP- 43, University of Edinburgh.I)e Smedt, Koenraad, and Keinpen, Gerard. (1991).Segment grammar: A fornmlism for incrementalsentence generation, in N a t u r a l L a n g u a g e G e n -e T n l i o n i n A r t i J i e i a l I n t e l l i g e n c e a n d C o m p u t a -

t i o n a l L i n gu i s t i c s . Edited by Cdcile L. Paris,William R. Swartout, and William C. Mann,Khlwer Academic Publishers, 329-349.Finkler, ~Volfgang, and Schauder, Ann. (1992). Effectsof incrementM output on incrementM natural lan-guage generation, ht Proc. of 10th ECAI, 505-507.Grosz, Barbara J., and Sidner, Candace L. (1986). At-tention~ intentions~ and the structure of discourse.C o m p u t a t i o n a l L i n g u i s t i c s , 12, 175-204.lIalliday, M. A. K. (1994). A n In t r o du c t i o n to l, 'un c -l i o n a l G r a m m a r . Fdward Arnold.]lovy, F,duard II. (] 993). Automated discourse gener-ation using discourse structure relations. A r t i f i c i a lI n t e l l i gen ce , 63, 34t-385.Kempen, Gerard, and Iloenkamp, Edward. (1987). Anincremental procedural grammar for sentence for-mulation. Co gn i t i v e Sc i en ce , 11, 201-258.Levelt, Willem J. M. (1989). S p e a k i n g : P r o m I n te n -t i o n s t o A r t i cu la t i o n . The MIT Press.Mann, Will iam C., and TholnI)son Sandra A. (1988).Rhetorical structure theory: Towards a functionaltheory of text organizatiou. T ex t , 8(3), 243-281.Moore, Johanna D., and Paris, Cdcile L. (1994). Plan-ning text for advisory dialogues: capturing inten-tional aim rhetorical information. C o m p u t a t i o n a lL i n g u i s t i c s , 19(4), 651-694.Nakano, Mikio. (1991). Constraint projection: An ettl-cient treatment of disjunctive feature descriptions.

In P r o c . o f 2 9 th A C L , 307-314.Reithinger, Norbert. (1992). The performance of anincrementM generation for multi-modM dialog con-tributions. In A s p e c t s o f A u t o m a t e d N a t u r a l La n-g u a g e G e n e r a t i o n . Edited by Robert Dale, Ell-uard tlovy, l)ietmar RSsner, and Oliviero Stock,Springer-Verlag, 263-276.Russel, Stuart, and Norvig, Peter. (1995). A r t i f i c i a lI n t e ll i g e n ce : A M o d e r n A p p r o a c h . Prentice IIall.Walker, Marilyn A., and Rainbow, Owen. (1994). Therole of cognitive modeling in achieving communica-tive intentions. In P r o e . o f 7t h I n t e r n a t i o n a l C o n -f e r e n c e o n N a t u r a l L a n g u a g e G e n e r a t i o n .

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utterance production computational model

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