ATTENTION, INTENTIONS, AND THE STRUCTURE OF DISCOURSE Barbara J. Grosz Artificial Intelligence Center and Center for the Study of Language and Information SRI International Menlo Park, CA 94025 Candace L. Sidner BB N Laboratories Inc. Cambridge, MA 02238 In this paper we explore a new theory of discourse structure that stresses the role of purpose and processing in discourse. In this theory, discourse structure is composed of three separate but interre- lated components: the structure of the sequence of utterances (called the linguistic structure), a struc- ture of purposes (called the intentional structure), and the state of focus of attention (called the attentional state). The linguistic structure consists of segments of the discourse into which the utter- ances naturally aggregate. The intentional structure captures the discourse-relevant purposes, expressed in each of the linguistic segments as well as relationships among them. The attentional state is an abstraction of the focus of attention of the participants as the discourse unfolds. The attentional state, being dynamic, records the objects, properties, and relations that are salient at each point of the discourse. The distinction among these components is essential to provide an adequate explanation of such discourse phenomena as cue phrases, referring expressions, and interruptions. The theory of attention, intention, and aggregation of utterances is illustrated in the paper with a number of example discourses. Various properties of discourse are described, and explanations for the behavior of cue phrases, referring expressions, and interruptions are explored. This theory provides a fram ework for describing the processing of utterances in a discourse. Discourse processing requires recognizing how the utterances of the discourse aggregate into segments, recognizing the intentions expressed in the discourse and the relationships among intentions, and track- ing the discourse through the operation of the mechanisms associated with attentional state. This processing description specifies in these recognition tasks the role of information from the discourse and from the participants' knowledge of the domain. 1 INTRODUCTION This paper presents the basic elements of a com puta- tional theory of discourse structure that simpfifies and expands upon previous work. By specifying the basic units a discourse comprises and the ways in which they can relate, a proper account of discourse structure provides the basis for an account of discourse meaning. An account of discourse structure also plays a central role in language processing because it stipulates constraints on those portions of a discourse to which any given utterance in the discourse must be related. An account of discourse structure is closely related to two questions: W hat individuates a discourse? What makes it coherent? That is, faced with a sequence of utterances, how does one know whether they constitute a single discourse, several (perhaps interleaved) discourses, or none? As we develop it, the theory of discourse struc- ture will be seen to be intimately connected with two nonlinguistic notions: intention and attention. Attention is an essential factor in explicating the processing of utterances in discourse. Intentions play a primary role in explaining discourse structure, defining discourse coher- ence, and providing a coherent conceptualization of the term discourse itself. Copyright 1986 by the Association for Computational Linguistics. Permission to copy without fee all or part of this material is granted provided that the copies are not made for direct commercial advantage and the CL reference and this copyright notice are included on the first page. To copy otherwise, or to republish, requires a fee and/or specific permission. 0362-613X/86/030175-204503.00 Computational Linguistics, Volume 12, Number 3, ~luly-September 1986 175
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
A T T E N T I O N , I N T E N T I O N S , A N D T H E S T R U C T U R E O F D I S C O U R S E
B a r b a r a J . G r o s z
A r t i f i c i a l I n t e l l i g e n c e C e n t e r a n d
C e n t e r f o r t h e S t u d y o f L a n g u a g e a n d I n f o r m a t i o n
S R I I n t e r n at i o n a l
M e n l o P a r k, C A 9 4 0 2 5
C a n d a c e L . S i d n e r
B B N L a b o r a t o r i e s I n c .
C a m b r i d g e , M A 0 2 2 3 8
I n t h i s p a p e r w e e x p l o r e a n e w t h e o r y o f d i s c o u r s e s t r u c t u r e t h a t s t r e s s e s t h e r o l e o f p u r p o s e a n d
p r o c e s s i n g i n d i s c o u r se . I n t h is t h e o r y , d i s c o u r s e s t r u c t u r e i s c o m p o s e d o f t h r e e s e p a r a t e b u t i n t e r r e -
l a t e d c o m p o n e n t s : t h e s t r u c t u r e o f t h e s e q u e n c e o f u t t e r a n c e s ( c a l l e d t h e l i n g u i s t i c s t r u c t u r e ) , a s t r u c -
t u r e o f p u r p o s e s ( c a l l e d t h e i n t e n t i o n a l s t r u c t u r e ) , a n d t h e s t a t e o f f o c u s o f a t t e n t i o n ( c a l l e d t h e
at ten t ion a l s ta te ) . T h e l i n g u i s t i c s t r u c t u r e c o n s i s t s o f s e g m e n t s o f t h e d i s c o u r s e i n t o w h i c h t h e u t t e r -
a n c e s n a t u r a l ly a g g r e g a t e . T h e i n t e n t io n a l s t r u c t u r e c a p t u r e s t h e d i s c o u r s e - r e l e v a n t p u r p o s e s ,
e x p r e s s e d i n e a c h o f t h e l in g u is t ic s e g m e n t s a s w e ll a s r e l a t io n s h i p s a m o n g t h e m . T h e a t t e n t i o n a l s t a t e
i s a n a b s t r a c t i o n o f t h e f o c u s o f a t t e n t i o n o f t h e p a r t i c i p a n t s a s t h e d i s c o u r s e u n f o ld s . T h e a t t e n t i o n a l
s t a t e , b e i n g d y n a m i c , r e c o r d s t h e o b j e c t s , p r o p e r t i e s , a n d r e l a t i o n s t h a t a r e s a l i e n t a t e a c h p o i n t o f t h e
d i s c o u r s e . T h e d i s t i n c ti o n a m o n g t h e s e c o m p o n e n t s i s e s s e n t i a l t o p r o v i d e a n a d e q u a t e e x p l a n a t i o n o f
s u c h d i s c o u r s e p h e n o m e n a a s c u e p h r a s e s , r e f e r r i n g e x p r e s s i o n s , a n d i n t e r r u p t i o n s .
T h e t h e o r y o f attent ion , in tent ion , a n d a g g r e g a t i o n o f u t t e r a n c e s i s i l l u s t r a t e d i n t h e p a p e r w i t h a
n u m b e r o f e x a m p l e d i s c o u r se s . V a r i o u s p r o p e r t i e s o f d is c o u r s e a r e d e s c r i b e d , a n d e x p l a n a t i o n s f o r t h e
b e h a v i o r o f c u e p h r a s e s , r e f e r r i n g e x p r e s s i o n s , a n d i n t e r r u p t i o n s a r e e x p l o r e d .
T h i s t h e o r y p r o v i d e s a f r a m e w o r k f o r d e s c r i bi n g t h e p r o c e s s i n g o f u t t e r a n c e s i n a d i s c o u rs e .
D i s c o u r s e p r o c e s s i n g r e q u i r e s r e c o g n i z i n g h o w t h e u t t e r a n c e s o f t h e d i s c o u r s e a g g r e g a t e i n t o s e g m e n t s ,
r e c o g n i z in g t h e i n t e n t i o n s e x p r e s s e d i n t h e d i s c o u r s e a n d t h e r e l a t i o n s h ip s a m o n g i n te n t i o n s , a n d t r a c k -
i n g t h e d i s c o u rs e t h r o u g h t h e o p e r a t i o n o f t h e m e c h a n i s m s a s s o c i a t e d w i t h a t t e n t i o n a l s t a t e . T h i s
p r o c e s s i n g d e s c r i p t i o n s p e c i f i e s i n t h e s e r e c o g n i t i o n t a s k s t h e r o l e o f i n f o r m a t i o n f r o m t h e d i s c o u r s e
a n d f r o m t h e p a r t i c i p a n t s ' k n o w l e d g e o f t h e d o m a i n .
1 INTRODUCTION
p a p e r p r e s e n t s t h e b a si c e l e m e n t s o f a c o m p u t a -
t h a t s i m p f if i e s a n d
w o r k . B y s p e c i fy i n g t h e b a s i c
u t t e r a n c e i n t h e d i s c o u rs e m u s t b e r e l a te d .
A n a c c o u n t o f d i s c o u r s e s t r u c t u r e i s c l o s e l y r e l a t e d t o
t w o q u e s t i on s : W h a t i n d i v i d u a t e s a d i s c o u r s e ? W h a t
m a k e s i t c o h e r e n t ? T h a t i s , f a c e d w i t h a s e q u e n c e o f
u t t e ra n c e s , h o w d o e s o n e k n o w w h e t h e r t h e y c o n s t it u t e a
s i n gl e d i sc o u r s e , s e v e r a l ( p e r h a p s i n t e r l e a v e d ) d i s c o u r s e s ,
o r n o n e ? A s w e d e v e l o p i t, t h e t h e o r y o f d i s c o u rs e s t r u c -
t u r e w i l l b e s e e n t o b e i n t i m a t e l y c o n n e c t e d w i t h t w o
n o n l i ng u i s ti c n o ti o n s : i n t e n t io n a n d a t t e n t io n . A t t e n t i o n
i s a n e s s e n t i a l f a c t o r i n e x p l i c a t i n g t h e p r o c e s s i n g o f
u t t e r a n c e s i n d i s c o u r se . I n t e n t i o n s p l a y a p r i m a r y r o l e i n
e x p l a i n i n g d i s c o u r s e s t r u c t u r e , d e f i n i n g d i s c o u r s e c o h e r -
e n c e , a n d p r o v i d i n g a c o h e r e n t c o n c e p t u a l i z a t i o n o f t h e
t e r m d i s c o u r s e i t s e l f .
h t 1 9 8 6 b y t h e A s s o c i a t i o n f o r C o m p u t a t i o n a l L i n g u i s t i c s. P e r m i s s i o n t o c o p y w i t h o u t f e e a l l o r p a r t o f t h i s m a t e r i a l is g r a n t e d p r o v i d e d t h a t
CL r e f e r e n c e a n d t h i s c o p y r i g h t n o t i c e a r e in c l u d e d o n t h e f i rs t p a ge . T o c o p y
e s a f e e a n d / o r s p e c if i c p e r m i s s io n .
B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
DPs and DSPs are basically the same sorts of
intentions. If an intention is a DP, then its satisfaction is a
main purpose of the discourse, whereas if it is a DSP,
then its satisfaction contributes to the satisfaction of the
DP. The following are some of the types of intentions
that could serve as DP/DSPs, followed by one example of
each type.
1. Intend that some agent intend to perfor m some phys-
ical task. Examp le: I n t e n d t h a t R u t h i n t e n d to f i x t h e
f l a t t ir e .
2. Intend that some agent believe some fact. Example:
I n t e n d t h a t R u t h b e l ie v e t h e c a m p f i r e h a s s t ar t e d.
3. Intend that some agent believe that one fact supports
another. Example:
l n t e n d t h a t R u t h b e l i e v e t h e s m e l l
o f s m o k e p r o v i d e s e v i d e n c e t h a t t h e c a m p f i r e i s s t a rt e d .
4. Intend that some agent intend to identify an object
B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
D I S C O U R SE S E G M E N T S
F O C U S S P A C E S T A C K
D O M I N A N C E H I E R A R C H Y
f ~
DS1
D S 2 ~,M,
,tM m i. l h ,i. /
~ Il l . /~. IW
D S 3 a . J
T E X T G I V E S
R I S E T O F S 2
T E X T G I V E ~ , ~
% RISE T O F S1
P R O P E R T I E S
O B J E C T S
R E L A T I O N S
DSP 2
F S 2
P R O P E R T I E S
O B J E C T S
R E L A T I O N S
DSP 1
F S l
D S P 1 D O M I N A T E S D S P 2
( a )
D I S C O U R SE S E G M E N T S
F O C U S S P A C E S T A C K
D O M I N A N C E H I E R A R C H Y
~ ' l ~ T E XT G IV E S
DS1 ~ . ~ R I E T F
~ - ~'* ~'~.I S 0 S~
D S 2 ~ , ~ /
• - - ' - \ T : X ; TO F >
P R O P E R T I E S
O B J E C T S
R E L A T I O N S
DSP 3
F S3
P R O P E R T I E S
O B J E C T S
R E L A T I O N S
DSP 1
F S l
D S P 1 D O M I N A T E S D S P 3
D S P 1 D O M I N A T E S D S P 2
( b )
F i g u re 1 . D i s c o u r s e S e g m e n t s , F o c u s S p a c e s a n d D o m i n a n c e H i e r a rc h y .
C o m p u t at io n a l L i n g u is t ic s , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r 1 9 8 6 1 8 1
B a r b a r a J. Grosz a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
S e v e r a l r e s e a r c h e r s ( e .g . , L i n d e a n d G o g u e n 1 9 7 8 ,
R e i c h m a n - A d a r 1 9 8 4 ) m i s i n t e r p r e t e d t h e o r i g i n a l
r e s e a r c h i n a n u n f o r t u n a t e a n d u n i n t e n d e d w a y : t h e y
t o o k t h e f o c u s - s p a c e h i e r a r c h y t o i n c l u d e ( o r b e i d e n t i c a l
t o ) t h e t a s k st r u c tu r e . T h e c o n f l a t i o n o f th e s e t w o s t r u c -
t u r e s f o r c e s a s in g le s t r u c t u r e t o c o n t a i n i n f o r m a t i o n
a b o u t a t t e n t i o n a l s t a t e , i n t e n t i o n a l r e l a t io n s h i p s , a n d
g e n e r a l t a sk , k n o w l e d g e . I t p r e v e n t s a t h e o r y f r o m
a c c o u n t i n g a d e q u a t e l y f o r c e r t a i n a s p e c t s o f d i s c o u r s e ,
i n c l u d i n g i n t e r r u p t i o n s ( s e e S e c t i o n 5 ) .
A s e c o n d i n s t a n c e o f c o n f u s i o n w a s t o i n f e r ( i n c o r -
r e c t l y ) t h a t t h e t a s k s t r u c t u r e w a s n e c e s s a r i l y a p r e b u i l t
t r e e . I f t h e t a s k s t r u c t u r e i s t a k e n t o b e a s p e c i a l c a s e o f
i n t e n t i o n a l s t r u c t u re , i t b e c o m e s c l e a r t h a t t h e t r e e s t r u c -
t u r e i s s i m p l y a m o r e c o n s t r a i n e d s t r u c t u r e t h a n o n e
m i g h t r e q u i re f o r o t h e r d i s c o u r se s ; t h e n a t u r e o f t h e t a s k
r e l a t e d t o t h e t a s k - o r i e n t e d d i s c o u r s e i s s u c h t h a t t h e
d o m i n a n c e h ie r ~ ir c hy o f t h e i n t e n t i o n a l s t r u c t u r e o f t h e
d i a lo g u e h a s b o t h d o m i n a n c e a n d s a t i s f a c t i o n - p re c e d e n c e
r e l a t io n s h i p s , 5 w h i l e o t h e r d i s c o u r s e s m a y n o t e x h i b i t
s i g n i f i c a n t p r e c e d e n c e c o n s t r a i n t s a m o n g t h e D S P s .
F u r t h e r m o r e , t h e r e h a s n e v e r b e e n a n y r e a s o n t o a s s u m e
t h a t t h e t a s k s t r u c t u r e s i n t a s k - o r i e n t e d d i a l o g u e s a r e
p r e b u i lt , a n y m o r e t h a n t h e i n t e n t i o n a l s t r u c t u r e o f a n y
o t h e r k i n d o f d i s c o u r s e s. I t i s r a t h e r t h a t o n e o b j e c t i v e o f
d i s c o u r s e t h e o r y ( n o t a t o p i c c o n s i d e r e d h e r e , h o w e v e r )
i s t o e x p l a i n h o w t h e O C P b u i l d s u p a m o d e l o f t h e t a s k
s t r u c t u r e b y u s i n g i n f o r m a t i o n s u p p l i e d i n t h e d i s c o u r s e .
H o w e v e r , i t i s i m p o r t a n t t o n o t e t h a t c o n f l a t i n g t h e
a f o r e m e n t i o n e d t w o r o l e s o f i n f o r m a t i o n a b o u t t h e t a s k
i t s e l f ( a s a p o r t i o n o f 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
a n d a s a s p e c i a l c a s e o f i n t e n t i o n a l s t r u c t u r e ) w a s r e g r e t -
t a b l e , a s i t f a i l s t o m a k e a n i m p o r t a n t d i s t i n c t i o n .
F u r t h e r m o r e , a s i s c l e a r w h e n i n t e n t i o n a l s t r u c t u r e s a r e
c o n s i d e r e d m o r e g e n e r a ll y , s u c h a c o n f l a t i o n o f r o l e s
d o e s n o t a l lo w f o r d if f e r e n ce s b e t w e e n w h a t o n e k n o w s
a b o u t a t a s k a n d o n e ' s i n t e n t i o n s f o r ( o r w h a t o n e m a k e s
e x p l ic i t in d i s c o u r s e a b o u t ) p e r f o r m i n g a t a s k .
I n s u m m a r y , t h e f o c u s i n g s t r u c t u r e i s t h e c e n t r a l
r e p o s i t o r y f o r t h e c o n t e x t u a l i n f o r m a t i o n n e e d e d t o p r o c -
e s s u t t e r a n c e s a t e a c h p o i n t i n t h e d i s c o u r s e . I t d i s t i n -
g u i s h e s t h o s e o b j e c t s , p r o p e r t i e s , a n d r e l a t i o n s t h a t a r e
m o s t s a l i e n t a t t h a t p o i n t a n d , m o r e o v e r , h a s l i n k s t o
r e l e v a n t p a r t s o f b o t h t h e l in g u is t ic a n d i n t e n t i o n a l s t r u c -
t u r e s. D u r i n g a d i s c ou r s e , a n in c r e a s i n g a m o u n t o f i n f o r -
m a t i o n , o n l y s o m e o f w h i c h c o n t i n u e s t o b e n e e d e d f o r
t h e i n t e r p r e t a t i o n o f s u b s e q u e n t u t t e r a n c e s , i s d i s c u s se d .
H e n c e , i t b e c o m e s m o r e a n d m o r e n e c e s s a r y t o b e a b l e
t o i d e n t i f y r e l e v a n t d i s c o u r s e s e g m e n t s , t h e e n t i t i e s t h e y
m a k e s a l i e nt , a n d th e i r D S P s. T h e r o l e o f a t t e n t i o n a l
s t a t e i n d e l i n e a t i n g t h e i n f o r m a t i o n n e c e s s a r y f o r u n d e r -
s t a n d i n g i s t h u s c e n t r a l t o d i s c o u r s e p r o c e s s i n g .
3 T w o E X A M PL E S
T o i l l u s t r a t e t h e b a s i c t h e o r y w e h a v e j u s t s k e t c h e d , w e
w i l l g i v e a b r i e f a n a l y s i s o f t w o k i n d s o f d i s c o u r s e : a n
a r g u m e n t f r o m a r h e t o r i c t e x t a n d ~i t a s k - o r i e n t e d
d i a l o g u e . F o r e a c h e x a m p l e w e d i s c u s s t h e s e g m e n t a t i o n
o f t h e d i s c o u r s e , t h e i n t e n t i o n s t h a t u n d e r l i e t h i s s e g m e n -
t a t i o n , a n d t h e r e l a t i o n s h i p s a m o n g t h e v a r i o u s D S P s . I n
e a c h c a s e , w e p o i n t o u t s o m e o f t h e l i n g u i s t i c d e v i c e s
u s e d t o i n d i c a t e s e g m e n t b o u n d a r i e s a s w e l l a s s o m e o f
t h e e x p r e s s i o n s w h o s e i n t e r p r e t a t i o n s d e p e n d o n t h o s e
b o u n d a r i e s . T h e a n a l y s i s is c o n c e r n e d w i t h s p e c i f y i n g
c e r t a i n a s p e c t s o f t h e b e h a v i o r t o b e e x p l i c a t e d b y a
t h e o r y o f d i sc o u r s e ; t h e r e m a i n d e r o f t h e p a p e r p r o v i d e s
a p a r t i a l a c c o u n t o f t h is b e h a v i o r .
3.1 AN ARGUME NT
O u r f i r s t e x a m p l e i s a n a r g u m e n t t a k e n f r o m a r h e t o r i c
t d x t ( H o l m e s a n d G a l l a g h e r 1 9 1 76 ) . I t i s a n e x a m p l e u s e d
b y C o h e n ( 1 9 8 3 ) i n h e r w o r k o n t h e s t r u c t u r e o f a r g u -
m e n t s . F i g u r e 2 s h o w s t h e d i a l o g u e a n d t h e e i g h t
d i s c o u r s e s e g m e n t s o f w h i c h i t i s c o m p o s e d . T h e d i v i s i o n
o f t h e a r g u m e n t i n to s e p a r a t e ( n u m b e r e d ) c l a u s e s i s
C o h e n ' s , b u t o u r a n a l y s i s o f t h e d i s c o u r s e s t r u c t u r e i s
d i f f e r e n t , s in c e i n C o h e n ' s a n a l y s i s , e v e r y u t t e r a n c e i s
d i r e c t l y s u b o r d i n a t e d t o a n o t h e r u t t e r a n c e , a n d t h e r e i s
o n l y o n e s t r u c t u r e t o e n c o d e l i n g u i s t i c s e g m e n t a t i o n a n d
t h e p u r p o s e s o f u t t e r a n c e s . A l t h o u g h b o t h a n a l y s e s
s e g m e n t u t t e r a n c e ( 4 ) s e p a r a t e l y f r o m u t t e r a n c e s ( 1 - 3 ) ,
s o m e r e a d e r s p l a c e t h i s u t t e r a n c e i n D S1 w i t h u t t e r a n c e s
( 1 ) t h r o u g h ( 3 ) ; t h i s is a n e x a m p l e o f t h e k i n d o f d i s a -
g r e e m e n t a b o u t b o u n d a r y u t t e r a n c e s f o u n d i n M a n n ' s
d a t a ( a s d i s c u s s e d i n S e c t i o n 2 . 1 ). T h e t w o p l a c e m e n t s
l e a d t o s l i g h t l y d i f f e r e n t D S P s , b u t n o t t o r a d i c a l l y d i f f e r -
e n t i n t e n ti o n a l s t r uc t u r e s . B e c a u s e t h e d i ff e r e n c e s d o n o t
a f f e c t t h e m a j o r t h r u s t o f t h e a r g u m e n t , w e w i l l d i s c u s s
o n l y o n e s e g m e n t a t i o n .
182
C o m p u t a t i o n a l L i n g u i s t ic s , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r
B a r b a r a J. Grosz a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t io n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
F i g u r e 3 l is t s t h e p r i m a r y c o m p o n e n t o f t h e D S P f o r
e a c h o f t h e s e s e g m e n t s a n d F i g u r e 4 s h o w s t h e d o m i -
n a n c e r e l a t i o n s h ip s t h a t h ol d a m o n g t h e s e i nt e n t i o n s. I n
S e c t i o n 7 w e d i s c u s s a d d i t i o n a l c o m p o n e n t s o f t h e
d i s c o u r s e s e g m e n t p u r p o s e ; b e c a u s e t h e s e a d d i t i o n a l
c o m p o n e n t s a r e m o r e i m p o r t a n t f o r c o m p l e t e n e s s o f t he
t h e o r y t h a n f o r d e t e r m i n i n g t h e e s se n t i a l d o m i n a n c e a n d
s a t i s f a c t i o n - p r e c e d e n c e r e l a t i o n s h i p s b e t w e e n D S P s , w e
o m i t su c h d e ta i l s h e r e . R a t h e r t h a n c o m m i t o u r s e l v e s t o
a f o r m a l l a n g u a g e i n w h i c h t o e x p r e s s t h e i n t e n t i o n s o f
t h e d i s c o u r s e , w e w il l u s e a s h o r t h a n d n o t a t i o n a n d
E n g l i s h s e n t e n c e s t h a t a r e i n t e n d e d t o b e a g l o s s f o r a
f o r m a l s t a t e m e n t o f t h e a c t u a l i n t e n ti o n s .
I O : ( I n t e n d
I 1 : ( I n t e n d
I 2 : ( I n t e n d
1 3 : ( I n t e n d
1 4 : ( I n t e n d
1 5 : ( I n t e n d
I 6 : ( I n t e n d
1 7 : ( I n t e n d
I C P ( B el ie v e O C P P O ) )
w h e r e P O = t h e p r o p o s i t i o n t h a t p a r e n t s a n d t e a c h e r s s h o u l d g u a r d t h e y o u n g
f r o m o v e r i n d u l g e n c e i n th e m o v i e s .
I C P ( B e l i e ve O C P P 1 ) )
w h e r e P 1 = t h e p r o p o s i t i o n t h a t i t i s t i m e t o c o n s i d e r t h e e f f e c t o f m o v i e s o n
m i n d a n d m o r a l s .
I C P ( B e li e ve O C P P 2 ) )
w h e r e P 2 = t h e p r o p o s i t i o n t h a t y o u n g p e o p l e c a n n o t d r i n k i n t h r o u g h t h e i r e y e s
a c o n t i n u o u s s p e c t a c l e o f i n te n s e a n d s t r a i n e d a c t i v i t y w i t h o u t h a r m f u l e f f e c t s .
I C P ( B e li e ve O C P P 3 ) )
w h e r e P 3 - - t h e p r o p o s i t i o n t h a t i t i s u n d e n i a b l e t h a t g r e a t e d u c a t i o n a l a n d
e t h i c a l g a i n s m a y b e m a d e t h r o u g h t h e m o v i e s .
I C P ( B e l ie v e O C P P 4 ) )
w h e r e P 4 = t h e p r o p o s i t i o n t h a t a l t h o u g h t h e r e a r e g a i n s , t h e t o t a l r e s u l t o f
c o n t i n u o u s a n d i n d i s c r i m i n a t e a t t e n d a n c e a t m o v i e s is h a r m f u l .
I C P ( B e l ie v e O C P P 5 ) )
w h e r e P 5 = t h e p r o p o s i t i o n t h a t t h e c o n t e n t o f m o v i e s ( i. e ., t h e c h a r a c t e r o f t h e
p l a y s ) i s n o t t h e b e s t .
I C P ( B e l ie v e O C P P 6 ) )
w h e r e P 6 = t h e p r o p o s i t i o n t h a t t h e s t o ri e s ( i. e ., th e p l a y s ) i n m o v i e s a r e e x c i t -
i n g a n d o v e r - e m o t i o n a l .
I C P ( B e l ie v e O C P P 7 ) )
w h e r e P 7 = t h e p r o p o s it i o n th a t m o v i e s p o r t r a y s t r o n g e m o t i o n a n d b u f f o o n e r y
w h i l e n e g l e c t in g t h e q u i e t a n d r e a s o n a b l e a s p e c t s o f l i fe .
F i g u re 3. P r i m a r y i n te n t i o n s o f t h e D S P s f o r M o v i e s e s s a y .
I 0 D O M I 1
I 0 D O M 12
1 2 D O M 1 3
1 2 D O M 1 4
1 4 D O M 1 5
1 4 D O M 1 6
1 6 D O M 1 7
F i g u re 4 . D o m i n a n c e r e l a t i o n s h i p s f o r t h e D S P s o f t h e M o v i e s e s s a y .
B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
c o m e s f r o m g e n e r a l k n o w l e d g e , p e r c e p t u a l i n f o r m a t i o n ,
a n d t h e li k e. T h u s , a c o m b i n a t i o n o f i n f o r m a t i o n i s r e l e -
v a n t t o d e t e r m i n i n g 1 2 a n d 1 3 a n d t h e i r r e l a t i o n s h i p s t o
I 1 , i n c l u d i n g a l l o f t h e f o l l o w i n g : t h e f a c t t h a t I 1 is p a r t
o f t h e i n t e n t i o n a l s t r u c t u r e , t h e f a c t t h a t t h e a p p r e n t i c e i s
c u r r e n t l y w o r k i n g o n s a t i s f y i n g I 1 , t h e u t t e r a n c e - l e v e l
i n t e n t io n s o f u t t e r a n c e s ( 5 ) a n d ( 1 2 ) , a n d g e n e r a l k n o w -
l e d g e a b o u t t h e t a s k .
T h e s a t i s f a c t i o n - p r e c e d e n c e r e l a t i o n s a m o n g 1 2 , 1 3 ,
a n d 1 4 a r e n o t c o m m u n i c a t e d d i r e c t l y i n t h e d i a l o g u e ,
b u t , l i k e d o m i n a n c e r e l a t i o n s , d e p e n d o n d o m a i n k n o w -
l e d ge . O n e p i e c e o f r e l e v a n t k n o w l e d g e i s t h a t a s a t is f a c -
t i o n p r e c e d e n c e r e l a t i o n e x i s t s b e t w e e n l o o s e n i n g t h e
s e t s c r e w s a n d pu l l i n g o f f t h e f l y w h e e l . T h a t r e l a t i o n is
s h a r e d k n o w l e d g e t h a t i s s t a t e d d i r e c t l y
(F ir s t loosen . . . .
t h n p u l l ) .
T h e r e l a t io n , a l o n g w i t h t h e f a c t t h a t b o t h 1 2
a n d 1 3 c o n t r i b u t e t o l o o s e n i n g t h e s e t s c r e w s , a n d t h a t 1 4
c o n t r i b u t e s t o p u l l i n g o f f t h e f l y w h e e l , m a k e s i t p o s s i b l e
t o c o n c l u d e 1 3 S P 1 4 a n d 1 2 S P 14 . T o c o n c l u d e t h a t 1 2
S P 13 , t h e a p p r e n t i c e m u s t e m p l o y k n o w l e d g e o f h o w t o
g o a b o u t l o o s e n i n g s c r e w - l i k e o b j e c t s .
T h e d o m i n a n c e a n d s a t i s f a c t i o n - p r e c e d e n c e r e l a t i o n s
f o r t h i s t a s k - o r i e n t e d f r a g m e n t f o r m a t r e e o f i n t e n t i o n s
r a t h e r t h a n j u s t a p a r t i a l o r d e r i n g . I n g e n e r a l , h o w e v e r ,
f o r a n y f r a g m e n t , t a s k - o r i e n t e d o r o t h e r w i s e , t h i s i s n o t
n e c e s s a r y .
I t i s e s s e n t i a l t o n o t i c e t h a t t h e i n t e n t i o n a l s t r u c t u r e i s
n e i t h e r i d e n t i c a l t o n o r i s o m o r p h i c t o a g e n e r a l p l a n f o r
r e m o v i n g th e f l y w h e e l . I t i s n o t i d e n t ic a l b e c a u s e a p l a n
e n c o m p a s s e s m o r e t h a n a c o l l e c t i o n o f i n t e n t i o n s a n d
r e l a t i o n s h i p s b e t w e e n t h e m ( c o m p a r e P o l l a c k ' s ( 1 9 8 6 )
c r i ti q u e o f A I p l a n n i n g f o r m a l i s m s a s t h e b a s i s f o r i n f e r -
r i n g i n t e n t io n s i n d i s c o u r se ) . I t is n o t i s o m o r p h i c b e c a u s e
t h e i n t e n t i o n a l s t r u c t u r e h a s a d i f f e r e n t s u b s t r u c t u r e f r o m
t h e g e n e r a l p l a n f o r r e m o v i n g t h e f l y w h e e l . I n a d d i t io n
t o t h e i n t e n t i o n s a r i s i n g f r o m s t e p s i n t h e p l a n , t h e i n t e n -
t i o n a l s t r u c t u r e t y p i c a l l y c o n t a i n s D S P s c o r r e s p o n d i n g t o
i n t e n t i o n s g e n e r a t e d b y t h e p a r t i c u l a r e x e c u t i o n o f t h e
t a s k a n d t h e d i a l o gu e . F o r e x a m p l e , th e g e n e r a l p l a n f o r
t h e d i s a s s e m b l y o f a f ly w h e e l i n c l u d e s s u b p l a n s f o r l o o s -
e n i n g t h e s e t s c r e w s a n d p u l l in g o f f t h e w h e e l ; i t m i g h t
a l s o in c l u d e s u b p l a n s ( o f t h e l o o s e n i n g s t e p ) f o r f i n di n g
t h e s e t s c r e w s , f i n d i n g a t o o l w i t h w h i c h t o l o o s e n t h e
s c r e w s , a n d l o o s e n i n g e a c h s c r e w i n d i v i d u a l l y . H o w e v e r ,
t h i s p l a n w o u l d n o t c o n t a i n c o n t i n g e n c y s u b p l a n s f o r
w h a t t o d o w h e n o n e c a n n o t f i n d t h e s c r e w s o r r e a l i z e s
t h a t t h e a v a i l a b l e t o o l i s u n s a t i s f a c t o r y . I n t e n t i o n s I 2 a n d
I 3 s t e m f r o m d i f f i c u l t i e s e n c o u n t e r e d i n l o c a t i n g a n d
l o o s e n i n g t h e s e t s c re w s . T h u s , t h e i n te n t i o n a l s t r u c t u r e
f o r t h is f r a g m e n t i s n o t i s o m o r p h i c t o t h e g e n e r a l p l a n f o r
r e m o v i n g t h e f l y w h e e l .
U t t e r a n c e ( 1 8 ) o f f e r s a n o t h e r e x a m p l e o f t h e d i ff e r -
e n c e b e t w e e n t h e i n t e n t i o n a l s t r u c t u r e a n d a g e n e r a l p l a n
f o r th e t a s k . T h i s u t t e r a n c e i s p a r t o f D S 4 - n o t j u s t p a r t
o f DS 1 - e v e n t h o u g h i t c o n t a i n s r e f e r e n c e s t o m o r e t h a n
o n e s i n g l e p a r t o f t h e o v e r a l l t a s k ( w h i c h i s w h a t I 1 i s
a b o u t ) . I t f u n c t i o n s t o e s t a b l i s h a n e w D S P , 1 4 , a s m o s t
s a l ie n t . R a t h e r t h a n b e i n g r e g a r d e d a s a r e p o r t o n t h e
o v e r a l l s t a t u s o f t h e t a s k , t h e f i r s t c l a u s e i s b e s t s e e n a s
m o d i f y i n g t h e D S P . 8 W i t h i t, t h e a p p r e n t i c e t e l ls t h e
e x p e r t t h a t t h e t r o u b l e i n r e m o v i n g t h e w h e e l i s n o t w i t h
t h e s c r e w s . T h u s , a l t h o u g h g e n e r a l t a s k k n o w l e d g e i s
u s e d i n d e t e r m i n i n g t h e i n t e n t i o n a l s t r u c t u r e , i t i s n o t
id en t i ca l t o i t .
I n t h is d i a l o g u e , t h e r e a r e f e w e r i n s t a n c e s i n w h i c h c u e
p h r a s e s a r e e m p l o y e d t o i n d i c a t e s e g m e n t b o u n d a r i e s
t h a n o c c u r i n t h e m o v i e s e s sa y . T h e p r i m a r y e x a m p l e i s
t h e u s e o f
f i r s t
i n ( 1 ) t o m a r k t h e s t a r t o f th e s e g m e n t
a n d t o i n d i c a t e t h a t i t s D S P i s t h e f i r s t o f s e v e r a l
i n t e n t i o n s w h o s e s a t i s f a c t i o n w i ll c o n t r i b u t e t o s a t i s fy i n g
t h e l a r g e r d i s c o u r se o f w h i c h t h e y a r e a p a r t .
P r i m a r y I n t e n t i o n s :
I I ( I n t e n d
Exper t
( I n t e n d
Appren t ic e
( R e m o v e A f l y w h e e l ) ))
I 2 : ( I n t e n d A ( I n t e n d E (T e l l E A ( L o c a t i o n o t h e r s e t s c r e w ) ) ) )
I 3 : ( I n t e n d A ( I n t e n d E ( I d e n t if y E A a n o t h e r t o o l ) ) )
I 4 : ( I n t e n d A ( I n t e n d E ( T e l l E A ( H o w ( G e t o f f A w h e e l ) ) ) ) )
I 5 : ( I n t e n d E ( K n o w - H o w - t o A (U s e A w h e e l p u l l e r) ) )
D o m i n a n c e R e l a t i o n s h i p s :
I 1 D O M I 2
I 1 D O M I 3
I 1 D O M I 4
I 4 D O M I 5
S a t i s f a c t i o n - P r e c e d e n c e R e l a t i o n s h i p s :
I 2 S P I 3
I 2 S P I 4
I 3 S P I 4
Figure 6 . I n t e n t i o n a l s t r u c t u r e f o r th e t a s k - o r i e n t e d d i a l o g u e s e g m e n t .
C o m p u t a t i o n a l L i n g u i s t i c s , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r
B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
The dialogue includes a clear example of the influence
of discourse structure on referring expressions. The
phrase the screw in the center is used in (25) to refer to
the center screw of the wheelpuller, not one of the two
setscrews mentioned in (18). This use of the phrase is
possible because of the attentional state of the discourse
structure at the time the phrase is uttered.
4 PROCESSING ISSUES
In previous sections of the paper, we abstracted from the
cognitive states of the discourse participants. The various
components of discourse structure discussed so far are
properties of the discourse itself, not of the discourse
participants. To use the theory in constructing computa-
tional models requires determining how each of the indi-
vidual components projects onto the model of an
individual discourse participant. In this regard, the prin-
cipal issues include specifying
1. how the ICP indicates and the OCP recognizes the
beginning and end of a discourse segment,
2. how the OCP recognizes the discourse segment
purposes, and
3. how the focus space stack operates.
In essence, the OCP must judge for each utterance
whether it starts a new segment, ends the current one
(and possibly some of its embedding segments), or
contributes to the current one. The informatio n available
to the OCP for recognizing that an utterance starts a new
segment includes any explicit linguistic cues contained in
the utter ance (see Section 6 9 as well as the relatio nship
between its utterance-level intentions and the active DSPs
(i.e., those in some focus space that is still on the stack).
Likewise, the fact that an utterance ends a segment may
be indicated explicitly by linguistic cues or implicitly from
its utterance-level intentions and their relationship to
elements of the intentional structure. If neither of these is
the case, the utterance is part of the current segment.
Thus, intention recognition and focus space management
play key roles in processing. Moreover, they are also
related: the intentional structure is a primary factor in
determining focus space changes, and the focus space
structure helps constrain the intention recognition proc-
ess.
4.1 INTENTION RECOGNITIO N
The recognition of DP/DSPs is the central issue in the
computation al modeling of intentional structure. If, as
we have claimed, for the discourse to be coherent and
comprehensible, the OCP must be able to recognize both
the DP/DSPs 10 and relationships (dominanc e and satis-
faction-precedence) between them, then the question of
how the OCP does so is a crucial issue.
For the discourse as a whole, as well as for each of its
segments, the OCP must identify both the intention that
serves as the discourse segment purpose and its relation-
ship to other discourse-level intentions. In particular, the
OCP must be able to recognize which other DSPs that
specific intention dominates and is dominated by, and,
where relevant, with which other DSPs it has satisfac-
tion-pr ecedence relationships. Two issues that are
central to the recognition problem are what information
the OCP can utilize in effecting the recognition and at
what point in the discourse that information becomes
available.
An adequate computational model of the recognition
process depends critically on an adequate theory of
intention and action; this, of course, is a large research
problem in itself and one not restricted to matters of
discourse. The need to use such a model for discourse,
however, adds certain constraints on the adequacy of any
theory or model. Pollack (1986) describes several prop-
erties such theories and models must possess if they are
to be adequate for supporting recognition of intention in
single-utterance queries; she shows how current AI plan-
ning models are inadequate and proposes an alternative
planning formalism. The need to enable recognition of
discourse-level intentions leads to yet another set of
requirements.
As will become clear in what follows, the information
available to the OCP comes from a variety of sources.
Each of these can typically provide partial information
about the DSPs and their relationships. These s ources are
each partially constraining, but only in their ensemble do
they constrain in full. To the extent that more informa-
tion is furnished by any one source, commensurately less
is needed from the others. The overall processing model
must be one of constraint satisfaction that can operate on
partial information. It must allow for incrementally
constraining the range of possibilities on the basis of new
information that becomes available as the segment
progresses.
4.1.1 INFORMATION CONSTRAINING THE DSP
At least three different kinds of information play a role in
the determination of the DSP: specific linguistic markers,
utterance-level intentions, and general knowledge about
actions and objects in the domain of discourse. Eac h
plays a part in the OCP's recognition of the DSP and can
be utilized by the ICP to facilitate this recognition.
Cue phrases are the most distinguished linguistic
means that speakers have for indicating discourse
segment boundaries and conveying information about the
DSP. Recen t evidence by Hirschb erg and Pierre humber t
(i~986) suggests that certain intonational properties of
utterances also provide partial information about the DSP
relationships. Because some cue phrases may be used as
clausal connectors, there is a need to distinguish their
discourse use from their use in conveying propositional
conte nt at the utterance level. For example, the word bu
functions as a boundary marker in utterance (7) of the
discourse in Section 3.1, but it can also be used solely (as
in the current utterance) to convey propositional content
(e.g., the conjunction of two propositions) and serve to
B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
As discussed in Section 6, cue phrases can provide
information about dominance and satisfaction-prece-
dence relationships between segments' DSPs. However,
they may not completely specify which DSP dominates or
satisfaction-precedes the DSP of the segment they start.
Furthermore, cue phrases that explicitly convey informa-
tion only about the attentional structure (see Section 6)
may be ambiguous about the state to which attention is
to shift. For example, if there have been several inter-
ruptions (see Section 5), the phrase but anyway indicates
a return to some previously interrupted discourse, but
does not specify which one. Although cue phrases do not
completely specify a DSP, the information they provide is
useful in limiting the options to be considered.
The second kind of information the OCP has available
is the utterance-level intention of each utterance in the
discourse. As the discussion of the movies example
(Section 3.1) pointed out, the DSP may be identical to
the utterance-level intention of some utterance in the
segment. Alternatively, the DSP may combine the
intentions of several utterances, as is illustrated in the
following discourse segment:
I want you to ar range a trip for me to Palo Alto.
It will be for two weeks.
I only fly on TWA.
The DSP for this segment is, roughly, that the ICP
intends for the OCP to make (complete) trip arrange-
ments for the ICP to go to Palo Alto for two weeks,
under the constraint that any flights be on TWA. The
Gricean intentions for these three utterances are as
follows:
U t t e r a n c e I :
ICP intends that OCP believe that ICP
intends that OCP intend to make trip plans
for ICP to go to
Palo Alto
U t t e r a n c e 2 : ICP intends that OCP believe that ICP
intends OCP to believe that the trip will last
two weeks
U t t e r a n c e 3 :
ICP intends that OCP believe that ICP
intends OCP to believe that ICP flies only on
TWA
These intentions must be combined in some way to
produ ce the DSP. The proc ess is quite complex, since the
OCP must recognize that the reason for utterances 2 and
3 is not simply to have some new beliefs about the ICP,
but to use those beliefs in arranging the trip. While this
example fits the schema of a request followed by two
informings, schemata will not suffice to represent the
behavior as a general rule. A different sequence of utter-
ances with different utterance-level intentions can have
the same DSP; this is the case in the following segment:
S 1: Have I told you yet to arrange my trip to Palo Alto?
Remember that I will fly only on TWA. OK?
$2: OK.
$3: I'm planning on staying for two weeks.
It is possible for a sequence that consists of a request
followed by two informings not to result in a modifica-
tion of the trip plans. For example, in the following
sequence the third utterance results in changing the way
the arrangements are made, rather than constraining the
nature of the arrangements themselves.
I want you to arrange a two-week trip for me to Palo
Alto. I fly only on TWA. The rates go up tomorrow,
so you'll want to call today.
Not only is the contribution of utterance-level
intentions to DSPs complicated, but in some instances the
DSP for a segment may both constrain and be partially
determined by the Gricean intention for some utterance
in the segment. For example, the Gricean-intention for
utterance (15) in the movies example (Section 3.1) is
derived from a combination of facts about the utterance
itself, and from its place in the discourse. On the surfac e,
(15) appears to be a question addressed to the OCP; its
intention would be roughly that the ICP intends the OCP
to believe that the ICP wants to know how young people,
etc. But (15) is actually a rhetor ical questio n and has a
very different intention associated with it - namely, that
the ICP intends the OCP to believe proposition P2
(namely, that young people cannot drink in through their
eyes a continuous spectacle of intense and strained activ-
ity without harniful effects). In this example, this partic-
ular intention is also the primar y com pone nt of the DSP.
The third kind of information that plays a role in
determining the DP/DSPs is shared knowledge about
actions and objects in the domain of discourse. This
shared knowledge is especially important when the
linguistic markers and utterance-level intentions are
insufficient for determining the DSP precisely.
In Section 7 we introduce two relations, a s u p p o r t s
relation between propositions and a generates relation
between actions, and present two rules stating equiv-
alences; one links a dominance relation between two
DSPs with a supports relation between propositions and
the other links a dominance relation between DSPs to a
generates relation between actions. Use of these rules in
one direction allows for (partially) determining what
supports or generates relationship holds from the domi-
nance relationship. But the rules can be used in the oppo-
site direction also: if, from the content of utterances and
reasoning about the domain of discourse, a supports or
generates relationship can be determined, then the domi-
nates relationship between DSPs can be determined. In
such cases it is important to derive the dominance
relationship so that the appropriate intentional and atten-
tional structures are available for processing or determin-
ing the interpretation of the subsequent discourse.
From the perspective of recognition, a trade-off
implicit in the two equivalences is impor tant. If the ICP
makes the dominance relationship between two DSPs
explicit (e.g., with cue phrases), then the OCP can use
this information to help recognize the (ICP's beliefs
about the) supports relationship. Conversely, if the ICP's
utterances make clear the (ICP's beliefs about the)
supports or generates relationship, then the OCP can use
C o m p u t a t i o n a l L i n g u i s ti c s , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r
B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
A primary role of the focus space stack is to constrain
the range of DSPs considered as candidates for domi-
nation or satisfaction-precedence of the DSP of the
curre nt segment. Only those DSPs in some space on the
focusi ng stack are viable prospects. As a result of this
use of the focusing structure, the theory predicts that this
decision will be a local one with respect to attentional
state. Because two focus spaces may be close to each
other in the attentional structure without the discourse
segments they arise from necessarily being close to one
another and vice versa, this prediction corresponds to a
claim that locality in the focusing structure is what
matters to determination of the intentional structure.
A second role of the focusing structure is to constrain
the OCP's search for possible referents of definite noun
phrases and pronouns . To illustrate this role, we will
consider the phrase
the screw in the center
in utterance
(25) of the task-oriented dialogue of Section 3. The
focus stack configuration when utterance (25) is spoken
is shown in Figure 7. The stack contains (in bott om- to-
top order) focus spaces FSI, FS4, and FS5 for segments
DS1, DS4, and DS5, respective ly. Fo r DS5 the wheel pul-
ler is a focused entity, while for DS4 the two setscrews
are (because they are explicitly mentioned). The entities
in FS5 are considered before those in FS4 as potential
referents. The wheelpuller has three screws: two small
screws fasten the side arms, and a large screw in the
center is the main functioning part. As a result, this large
screw is implicitly in focus in FS5 (Grosz 1977) and thus
identified as the referent without the two setscrews ever
being considered.
Attentional state also constrains the search for refer-
ents of pronouns. Because pronouns contain less explicit
information about their referents than definite
descriptions, additional mechanisms are needed to
account for what may a nd may not be pronominalized in
the discourse. One such mechanis m is centering (which
we previously called immediate focusing; Grosz, Joshi,
and Weinstein 1983; Sidner 1979).
Centering, like focusing, is a dynamic behavior, but is
a more local phenom enon. In brief, a backwar d-looki ng
center is associated with each utterance in a discourse
segment; of all the focused elements the backward-look-
ing center is the one that is central in that utterance (i.e.,
the uttering of the particular sequence of words at that
point in the discourse). A combination of syntactic,
semantic, and discourse information is used to identify
the backward-looking center. The fact that some entity is
the backward-looking center is used to constrain the
search for the referent of a pronoun in a subsequent
uttera nce. Note that unlike the DSP, which is con sta nt
for a segment, the backward-looking center may shift:
different entities may become more salient at different
points in the segment.
The presence of both centers and DSPs in this theory
leads us to an intriguing conjecture: that topi c is a
concept that is used ambiguously for both the DSP of a
segment and the center. In the literature the concept of
topi c has appeare d in many guises. In syntactic form it
is used to describe the preposing of syntactic constituents
in English and the wa marking in Japanese. Resear ch-
ers have used it to describe the sentence topic (i.e., what
the sentence is about; Firbas 1971, Sgall, Haji~ov~, and
SETSCREWS 3
FLYWHEELIo
DSP 1
FS1
SCREW 1
SCREW 2
DSP 2
FS2
SETSCREWS 3
FLYWHEELIo
DSP 1
FS1
ALLEN WRENCH 9
KEYS14
DSP 3
FS3
SETSCREWS 3
FLYWHEELlo
DSP 1
FS1
WHEEL PULLER 8
DSP 5
FS5
SETSCREWS 3
FLYWHEELIo
DSP 4
FS4
SETSCREWS 3
FLYWHEELlo
DSP 1
FS1
t i m e
Figure 7. Focus Stack Transitions Leading up to Utteranc e (25).
C o m p u t a t i o n a l L i n g u i st i cs , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r 1 9 8 6 1 9 1
B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
man-Adar 1984) because the embedding occurs only in
the attentional structure. As shown in Figure 8, the
focus space for D2 is pushed onto the stack above the
focus space for D1, so that the focus space for D2 is
more salient than the one for D 1, until D2 is comple ted.
The intentional structures for the two segments are
distinct. There are two DP/DSP structures for the utter-
ances in this sequence - one for those in D1 an d the
other for those in D2. It is not necessary to relate these
two; indeed, from an intuitive point of view, they are not
related.
The focusing structure for true interruptions is differ-
ent from that for the normal embedding of segments,
because the focusing boundary between the interrupted
discourse and the in terru ption is impene trable . 12 (This is
depicted in the figure by a line with intersecting hash
marks betwee n focus spaces). The impenetrable bound a-
ry between the focus spaces prevents entities in the spac-
es below the boundary from being available to the spaces
above it. Because the second discourse shifts attention
totally to a new purpose (and may also shift the identity
of the intended hearers), the speaker cannot use any
DISCOURCESEGMENTS
FOCUSSPACESTACK
DOMINANCE HIERARCHY
DI : JOHNCAME BYAND
LEFT THE GROCERIES \
D2: STOP THA T YOU KIDS
D1 cont: AND I PUT THEM
AWAY AFTER HE LEFT
\
A
/
\
\
KIDS 1
KIDS 1 STOP ...
DSP 2
FS5
; - , - , ; - , - , , - . - - . ; - r. t
JOHN 10
GROCERIES14
JOHN'S COMING 15
DSP 1
FS4
(EMPTY)
a )
DISCOURSE SEGMENTS
FOCUS SPACE STACK
DOMINANCE HIERARCHY
f~
DI : JOHN CAME BY AND
LEFT THE GROCERIES
D2: STOP THA T YOU KIDS
D1 cont: AND I PUT THEM
AWAY AFTER HE LEFT
/
/
JOHNlo
GROCERIES14
JOHN'SCOMING15
DSP 1
FS4
(EMPTY)
b )
F i g u r e
8. The structures of a true interruption.
C o m p u t a t i o n a l L i n g u i s t ic s , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r 1 9 8 6 1 9 3
B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
referential expressions during it that depend on the
accessibility of entities fro m the first discourse. Since the
boundary between the focus space for D1 and the one
for D2 is impenetrable, if D2 were to include an utter-
ance such as
p u t t h e m a w a y ,
the pronoun would have to
refer deictically, and not anaphorically, to the groceries.
In this sample discourse, however, D1 is resumed
almost immediately. The pronoun
t h e m
in
a n d I p u t t h e m
a w a y
cannot refer to the children (the focus space for D2
has been popped from the stack), but only to the
groceries. For this to be clear to the OCP, the ICP must
indicate a retur n to D 1 explicitly. One linguistic indicator
in this example is the change of mood from imperative.
Indicators that the
s to p t h a t
utterance is an interruption
include the change to imperative mood and the use of the
vocative (Polanyi and Scha 1983). Two other indicators
may be assumed to have been present at the time of the
discourse - a chang e of into natio n (imagine a slightly
shrill tone of command with an undercurrent of annoy-
ance) and a shift of gaze (toward and then away from
the kids). It is also possible that the type of pause pres-
ent in such cases is evidence of the interruption, but
further research is needed to establish whether this is
indeed the case.
In contrast to previous accounts, we are not forced to
integrate these two discourses into a single grammatical
structure, or to answer questions about the specific
relationship between segments D2 and D1, as in
Reichman's model (Reichman-Adar 1984). Instead, the
intuition that readers have of an embedding in the
discourse structure is captured in the attentional state by
the stacking of focus spaces. In addition, a read er's intui-
tive impression of the distinctness of the two segments is
captured in their different intentional (DP/DSP) struc-
tures.
5 .3 T Y P E 2 : F L A S H B A C K S A N D F I L L IN G IN M I S S I N G P L A C E S
Sometimes an ICP interrupts the flow of discussion
because some purposes, propositions, or objects need to
be brought into the discourse but have not been: the ICP
forgot to include those entities first, and so must now go
back and fill in the missing inform ation. A flashback
segment occurs at that point in the discourse. The flash-
back is defined as a segment whose DSP satisfaction-pre-
cedes the interrupted segment and is dominated by some
othe r segme nt's DSP. Henc e, it is a specialization of the
weak definition of interruptions. This type of inter-
ruptio n differs fro m true interruptions both intentionally
and linguistically: the DSP for the flashback bears some
relationship to the DP for the whole discourse. The
linguistic indicator of the flashback typically includes a
comm ent about something going wrong. In addition the
audience always remains the same, whereas it may
change for a true interruption (as in the example of the'
previous section).
In the example below, taken from Sidner (1982), the
ICP is instructing a mock-up system (mimicked by a
person) about how to define and display certain informa-
tion in a particular knowledge-representation language.
Again the interruption is indicated by italics.
OK. Now how do I say that Bill is
W h o o p s I f o r g o t a b o u t A B C .
I n e e d a n i n d i v id u a l c o n c e p t f o r t h e c o m p a n y A B C
. . .[ r e m a i n d e r o f d i s c o u r se s e g m e n t o n A B C ] . . .
Now back to Bill. How do I say that Bill is an employee
of ABC?
The DP for the larger discourse from which this
sequence was taken is to provide information about vari-
ous companies (including ABC) and their employees.
The oute r segm ent in this example - DBill - has a DSP -
D S P B i l l - to tell about Bill, while the inner segment -
D A B C - - has a D S P - D S P A B C -- t o convey certain infor-
mation about ABC. Because of the nature of the infor-
mation being told, there is order in the final structure of
the DP/DSPs: information about ABC must be conveyed
before all of the information abou t Bill can be. The ICP
in this instance does not realize this constraint until after
he begins. The flas hbac k interruption allows him to
s a t i s f y D S P A B C while suspending satisfaction of D S P B i l l
(which he then resumes). Hence, there is an intentional
structure rooted at DP and with
D S P A B C
and
D S P B i u a s
o rd ered
sister nodes. The following three relationships
hold betwee n the differ ent DSPs:14
DP DOM DSPABC
DP DOM DSPBill
DSPABC SP DSPBill
This kind of interruption is distinct from a true inter-
ruption because there is a connection, although indirect,
between the DSPs for the two segments. Furthermore,
the linguistic features of the start of the interruption
signify that there is a precedence relation between these
DSPs (and hence that the correc tion is necessary). Flash-
backs are also distinct from normally embedded
discourses because of the precedence relationship
between the DSPs for the two segments and the order in
which the segments occur.
The available linguistic data permit three possible
attentional states as appropriate models for flashback-
type interruptions: one is identical to the state that would
ensue if the flashback segment were a normally embed-
ded segment, the second resembles the model of a true
interruption, and the third differs from the others by
requiring an auxiliary stack. An example of the stack for
a normally embedded sequence is given in Section 4.2
Figure 9 illustrates the last possibility. The focus space
for the flashbac k - FSABC -- is pushed onto the stack
after an appropriate number of spaces, including the
focus space for the outer segment - F S B i l l , have been
popped from the main stack and pushed onto an auxiliary
stack. All of the entities in the focus spaces remaining on
the main stack are normally accessible for reference, but
none of those on the auxiliary stack are. In the example
in the figure, entities in the spaces fro m FS A to FS B are
accessible as well (though less salient than) those ir/
1 9 4
C o m p u t a t i o n a l L i n g u i s t i c s , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r
B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
s p a c e F S A B C . E v i d e n c e f o r t h is k i n d o f s t a c k b e h a v i o r
c o u l d c o m e f r o m d i s c o u r s e s i n w h i c h p h r a s e s i n t h e
s e g m e n t a b o u t A B C c o u l d r e f e r t o e n t i t i e s r e p r e s e n t e d i n
F S B , b u t n o t t o t h o s e i n F S B i u o r F S C . A f t e r a n e x p l i c i t
i n d i ca t i o n t h a t t h e re i s a r e tu rn t o D S P B i l l ( e . g . , t h e Now
back to Bill u s e d i n t h i s e x a m p l e ) , a n y f o c u s s p a c e s l e f t
o n t h e s t a c k f r o m t h e f l a s h b a c k a r e p o p p e d o f f , a n d a l l
s p a c e s o n t h e a u x i l i a r y s t a c k ( i n c l u d i n g F SB il l ) a r e
r e t u r n e d t o t h e m a i n s t a c k . N o t e , h o w e v e r , t h a t t h i s
m o d e l d o e s n o t p r e c l u d e t h e p o s s i b i l i t y o f a r e t u r n t o
s o m e s p a c e b e t w e e n F S A a n d F S B b e f o r e p o p p i n g t h e
a u x i li a r y s t a c k . W h e t h e r t h e r e a r e d i s c o u r s e s t h a t i nc l u d e
s u c h a r e t u r n a n d a r e d e e m e d c o h e r e n t i s a n o p e n q u e s -
t i o n .
T h e a u x i l i a r y s t a c k m o d e l d i f f e r s f r o m t h e o t h e r t w o
m o d e l s b y t h e r e f e r e n c e s p e r m i t t e d a n d b y t h e s p a c e s
t h a t c a n b e p o p p e d t o . G i v e n t h e i n i t i a l c o n f i g u r a t i o n i n
F i g u r e 9 , i f t h e s e g m e n t w i t h D SP A B C w e r e n o r m a l l y
e m b e d d e d , F S AB C w o u l d j u s t b e a d d e d t o t h e t o p o f t h e
s t a c k . I f i t w e r e a t r u e i n t e r r u p t i o n , t h e s p a c e w o u l d a l s o
' b e a d d e d t o t h e s t a c k , b u t w i t h a n i m p e n e t r a b l e b o u n d a -
r y b e t w e e n i t a n d F S B il l. I n t h e n o r m a l s t a c k m o d e l , e n t i -
t i e s i n t h e s p a c e s l o w e r i n t h e s t a c k w o u l d b e a c c e s s i b l e ;
i n t h e t r u e i n t e r r u p t i o n t h e y w o u l d n o t . I n e i t h e r o f t h e s e
t w o m o d e l s , h o w e v e r , F SB ill w o u ld b e t h e s p a c e r e t u r n e d
t o f i r s t . T h e a u x i l i a r y s t a c k m o d e l i s o b v i o u s l y m o r e
c o m p l i c a t e d t h a n t h e o t h e r t w o a l te r n a t i v e s . W h e t h e r it
( o r s o m e e q u i v a l e n t a l t e r n a t i v e ) i s n e c e s s a r y d e p e n d s o n
f a c t s o f d i s c o u r s e b e h a v i o r t h a t h a v e n o t y e t b e e n d e t e r -
m i n e d .
5 .4 TYPE3: DIGRESSIONS
T h e t h i r d t y p e o f i n t e r r u p t i o n , w h i c h w e c a l l a d i g r e s s i o n ,
i s d e f i n e d a s a s t r o n g i n t e r r u p t i o n t h a t c o n t a i n s a r e f e r -
e n c e t o s o m e e n t i t y t h a t i s s a l i e n t i n b o t h t h e i n t e r r u p t i o n
a n d th e in t e r r u p t e d s e g m e n t . F o r e x a m p l e , i f w h i l e
d i s c u ss i n g B i ll 's r o le i n c o m p a n y A B C , o n e c o n v e r s a t i o n a l
p a r t i c i p a n t i n t e r r u p t s w i t h , Speaking of Bill, that reminds
me, he came to dinner last week, B i l l r e m a i n s s a l i e n t , b u t
t h e D P c h a n g e s . D i g r e s s i o n s c o m m o n l y b e g i n w i t h
p h r a s e s s u c h a s speaking of John o r that reminds me,
a l t h o u g h n o c u e p h r a s e n e e d b e p r e s e n t , a n d that reminds
me m a y a l s o s ig n a l o t h e r s t a c k a n d i n t e n t i o n s h i ft s .
I n t h e p r o c e s s i n g o f d i g r e s s i o n s , t h e d i s c o u r s e - l e v e l
i n t e n t i o n o f t h e d i g r e s s io n f o r m s t h e b a s e o f a s e p a r a t e
i n t e n t i o n a l s t r u c t u r e , j u s t a s i n t h e c a s e o f t r u e i n t e r -
r u p t i o n s . A n e w f o c u s s p a c e i s f o r m e d a n d p u s h e d o n t o
t h e s t a c k , b u t i t c o n t a i n s a t l e a s t o n e - a n d p o s s i b l y o t h e r
- e n t i ti e s f r o m t h e i n t e r r u p t e d s e g m e n t ' s f o c u s s p a ce .
L i k e t h e f l a s h b a c k - t y p e i n t e r r u p t i o n , t h e d i g r e s s i o n m u s t
u s u a l l y b e c l o s e d w i t h a n e x p l i c i t u t t e r a n c e s u c h a s
getting back to ABC... o r anyway.
M A I N
S T A C K
F S B I L L
FS C
F S B
FS A
M A I N A U X I L I A R Y
S T A C K S T A C K
F SAB c
FS B
FS A
F SBI LL
FS c
t i m e
S T A C K A T t I S T A C K S A T t 2
F i g u r e
9 . T h e a u x i l ia r y s t a c k m o d e l f o r f l a s h b a c k s .
C o m p u t a t i o n a l
L i n g ui s ti c s, V o lu m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r 1 9 8 6
B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
5.5 NONINTERRUPTIONS - SEMANTIC RETURNS
One case of discourse behavior that we must distinguish
comprises the so-called semantic returns observed by
Reichman (1981) and discussed by Polanyi and Scha
(1983). In all the interruptions we have considered so
far, the stack must be popped when the interruption is
over and the interrupted discourse is resumed. The focus
space for the interrupted segment is return ed to. In the
case of semantic returns, entities and DSPs that were sali-
ent during a discourse in the past are taken up once
again, but are explicitly reintroduced. For example,
suppose that yesterday two people discussed how badly
Jack was behaving at the party; then today one of them
says
R e m e m b e r o u r d i sc u s s io n a b o u t J a c k a t t h e p a r t y ?
W e l l , a l o t o f o t h e r p e o p l e t h o u g h t h e a c t e d j u s t a s b a d l y a s
w e th o u g h t h e d id . The utterances today recall, or return
to, yesterday's conversation to help satisfy the intention
that more be said about Jack's poor behavior.
Anything that can be talked about once can be talked
about again. However, if there is no focus space on the
stack corresponding to the segment and DSP being
discussed further, then, as Polanyi and Scha (1983) point
out, there is no popping of the stack. There need not be
any discourse underway when a semantic return occurs;
in such cases, the focus stack will be empty. Thus, unlike
the returns that follow normal
returns involve a push onto the
containing, among other things,
reintroduced entities.
interruptions, semantic
stack of a new space
representations of the
The separation of attentional state from intentional
structure makes clear not only what is occurring in such
cases, but also the intuitions underlying the term seman-
tic return. In reintroducing some entities fr om a previous
discourse, conversational participants are establishing
some connection between the DSP of the new segment
and the intentional structure of the original discourse. It
is not a return to a previous focus space because the
focus space for the original discourse is gone from the
stack, and the items to be referred to must be re-establ-
ished explicitly. For example, the initial refe rence to
Jack in the preceding example cannot be accomplished
with a pronoun; with no prior mention of Jack in the
current discussion, one cannot say,
R e m e m b e r o u r
d i sc u ss io n a b o u t h im a t t h e p a r t y .
The intuitive
impression of a return in the strict sense is only a return
to a previous intentional structure.
6 APPLICATION OF THE THEORY: CUE WORD S
Both attentional state and intentional structure change
during a discourse. ICPs rarely change attention by
directly and explicitly referring to attentional state (e.g.,
using the phrase
N o w l e t ' s t u r n o u r a t t e n t i o n t o . . . ) .
Like-
wise, discourses only occasionally include an explicit
reference to a change in purpose (e.g., with an utterance
such as
N o w I w a n t to e x p la i n t h e t h e o r y o f d y n a m i c
p r o g r a m m i n g ) .
More typically, ICPs employ indirect
means of indicating that a change is coming and what
kind of change it is. Cue phrases provide abbreviated,
indirect means of indicating these changes.
In all discourse changes, the ICP must provide infor-
mation that allows the OCP to determine all of the
following:
1. that a change of attention is imminent;
2. whether the change returns to a previous focus space
or creates a new one;
3. how the intention is related to other intentions;
4. what preceden ce relationships, if any, are relevant;
5. what intention is entering into focus.
Cue phrases can pack in all of this information, except
for (5). In this section, we explore the predictions of our
discourse structure theory about different uses of these
phrases and the explanations the theory offers for their
various roles.
We use the configuration of attentional state and
intentional structure illustrated in Figure 10 as the start-
ing point of our analysis. In the initial configuration, the
focus space stack has a space with DSP X at the bottom
and another space with DSP A at the top. The intentional
structure includes the information that X dominates A.
From this initial configuration, a wide variety of moves
may be made. We examine several changes and the cue
phrases that can indicate each of them. Because these
phrases and words in isolation may ambiguously play
either discourse or other functional roles, we also discuss
the other uses whenever appropriate. Furthe rmor e, cue
phrases do not function unambiguously with respect to a
particular discourse role. Thus for example,
f i r s t
can be
used for two different moves that we discuss below.
First, consider what happens when the ICP shifts to a
new DSP, B, that is dominated by A (and corresponding-
ly by X). The dominanc e relationship between A and B
becom es part of the intentional structure. In addition,
the change in DSP results in a change in the focus stack.
The focus stack models this change, which we call n e w
d o m i n a n c e , by a having new space pushed onto the stack
with B as the DSP of that space (as illustrated in Figure
11). The space cont ainin g A is salient, but less so than
the space with B. Cue phrase(s) to signal this case, and
only this one, must communicate two pieces of informa-
tion: that there is a change to som e new purpo se (result-
ing in a new focus space being created in the attentional
state model rather than a return to one on the stack) and
that the new purpose (DSP B) is dominated by DSP A.
Typical cue phrases for this kind of change are
f o r e x a m -
p l e
and
to wi t ,
and sometimes
f i r s t
and
sec o n d .
Cue phrases can also exhibit the existence of a satis-
faction- precede nce relationship. If B is to be the first in
a list of DSPs dominated by A, then words such as
f i r s t
and
i n t h e f i r s t p l a c e
can be used to communicate this
fact. Later in the discourse, cue phrases such as
sec o n d ,
th ird ,
and
f i n a l l y
can be used to indicate DSPs that are
dominat ed by A and satisfaction-prece ded by B. In these
cases, the focus space containing B would be popped
196
C o m p u t a t i o n a l L i n g u i s t ic s , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r
B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
Cue phrases can also exhibit the satisfaction of a DSP,
and hence the completion of a discourse segment. The
completion of a segment causes the current space to be
popped from the stack. There are many means of
linguistically marking completions. In texts, paragraph
and chapter boundaries and explicit comments (e.g.
T h e
E n d ) are common. In conversations, completion can be
indicated either with cue phrases such as
f i n e
or
O K 1 5
or
with more explicit references to the satisfaction of the
intention (e.g.,
T h a t ' s a l l f o r p o i n t 2 ,
or
T h e a y e s h a v e i t . ) .
Most cue phrases that communicate changes to atten-
tional state announce pops of the focus stack. However ,
at least one cue phrase can be construed to indicate a
push, namely, T h a t r e m i n d s m e . By itself, this phrase does
not specify any particular change in intentional structure,
but merel y shows that ther e will be a new DSP. Since
this is equivalent to indicating that a new focus space is
to be pushed onto the stack, this cue phrase is best seen
as conveying attentional information.
Cue phrases that indicate pops to some other space
back in the stack include
b u t a n y w a y , a n y w a y , i n a n y c a s e ,
and
n o w b a c k t o . . .
When the current focus space is
popped from the stack, a space already on the stack
becomes most salient. Fro m the configuration in Figure
10, the space with A is popped from the stack, perhaps
with others, and another space on the stack becomes the
top of the stack. Popping back changes the stack without
creating a new DSP, or a dominance or satisfaction-
precedence relationship. The pop entails a return to an
old DSP; no change is effected in the intentional struc-
ture.
There are cue phrases, such as
n o w
and
n e x t ,
that
signal a change of attentional state, but do not distinguish
between the creation of a new focus space and the return
to an old one. These words can be used for either move.
For example, in a task-oriented discourse during which
some task has been mentioned but put aside to ask a
question, the use of
n o w
indicates a change of focus. The
utterance following n o w , however, will either return the
discussion to the deferred task or will introduce some
new task for consideration.
Note, finally, that a pop of the focus stack may be
achieved without the use of cue phrases as in the follow-
ing fragment of a task-oriented dialogue (Grosz 1974):
A: One bolt is stuck, i'm trying to use both the pliers and
the wrench to get it unstuck, but I haven't had much
luck.
E: Don 't use pliers. Show me what you are doing.
A: I'm pointing at the bolts.
E: Show me the 1/2 combina tion wrench, please.
A: OK.
E: Good, now show me the 1/2 box wrench.
A: I already got it loosened.
The last utterance in this fragment returns the
discourse to the discussion of the unstuck bolt. The pop
can be inferred only from the content of the main portion
of the utterance. The pronou n (or, more accurately, the
fact that it cannot be referring to the wrench) is a cue
that a pop is needed, but only the reference to the loos-
ening action allows the OCP to recognize to which
discourse segment this utterance belongs, as discussed by
Sidner (1979) and Robinson (1981). A summary of the
uses of cue phrases is given in Figure 12.
Attentional Change
(push) now, next, that reminds me, and, but
(pop to) anyway, but anyway, in any case, now back to
(complete) the end, ok, fine, (paragrap h break)
True interruption
I must interrupt, excuse me
Flashbacks
Oops, I forgot.
Digressions
By the way, incidentally, speaking of,
Did you hear about .... That r eminds me
Satisfaction-precedes
in the first place, first, second, finally, moreover,
furthermore
New dominance
for example, to wit, first, second, and, moreover,
furthermore, therefore, finally
Figure 12. The uses of cue phrases.
1 9 8 C o mp u ta t io n a l L ing u is ti c s, V o lu me 1 2 , N u m b er 3 , J u ly - S ep temb er 1 98 6
B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
c e n t r a l ro l e . T h e D S P s a r e i n t e n d e d t o b e r e c o g n i z e d :
t h e y a c h i e v e t h e i r e f f e c t s , i n p a r t , b e c a u s e t h e O C P
r e c o g n i z e s t h e I C P ' s i n t e n t i o n f o r t h e O C P t o ~ t h a t p .
T h e O C P ' s r e c o g n i t i o n o f t h i s i n t e n t i o n i s c r u c i a l t o i t s
a c h i e v i n g t h e d e s i r e d e f f e c t . I n S e c t i o n 4 w e d e s c r i b e d
c e r t a i n c o n s t r a i n t s o n t h e r e c o g n i t i o n p r o c e s s .
7.1 THE BASIC GENERALIZATION
I n e x t e n d i n g G r i c e ' s a n a l y s is t o t h e d i s c o u r s e l e v e l , w e
h a v e t o c o n s i d e r n o t o n l y i n d i v i d u a l b e l i e f s a n d
i n t e n t io n s , b u t a l s o t he r e l a t i o n s h ip s a m o n g t h e m t h a t
a r i se b e c a u s e o f th e r e l a t i o n s h i p s a m o n g v a r i o u s
d i s c o u r s e s e g m e n t s ( a n d u t t e r a n c e s w i t h i n a s e g m e n t )
a n d t h e p u r p o s e s t h e s e g m e n t s s e r v e w i t h r e s p e c t t o t h e
e n t i r e d i s c o u r s e . T o c l a r i f y t h e s e r e l a t i o n s h i p s , c o n s i d e r
a n a n a l o g o u s s i t u a t i o n w i t h n o n l i n g u i s t i c a c t i o n s . 18 A n
a c t i o n m a y d i v id e i n t o s e v e r a l s u b a c t io n s ; f o r e x a m p l e ,
t h e p l a n t i n g o f a r o s e b u s h d i v i d e s i n t o p r e p a r i n g t h e s o i l ,
d i g g i n g a h o l e , p l a c i n g t h e r o s e b u s h i n t h e h o l e , f i l l i n g
t h e r e s t o f t h e h o l e w i t h s o i l , a n d w a t e r i n g t h e g r o u n d
a r o u n d t h e b u s h . T h e i n t e n t i o n t o p e r f o r m t h e p l a n t i n g
a c t i o n i n c l ud e s s e v e r a l s u b s i d i a r y in t e n t i o n s ( o n e f o r
e a c h o f t h e s u b a c t i o n s - n a m e l y , t o d o i t) .
I n d i s c o u r s e , i n a m a n n e r t h a t i s a n a l o g o u s t o n o n l i n -
g u i s t i c a c t i o n s , t h e D P ( a n d s o m e D S P s ) i n c l u d e s s e v e r a l
s u b s i d i a r y i n t e n t i o n s r e l a t e d t o t h e D S P s i t d o m i n a t e s .
F o r p u r p o s e s o f e x p o s i t i o n , w e w i l l u s e t h e t e r m p r i m a r y
i n t en t i on
t o d i s t in g u i s h t h e o v e r a l l i n t e n t i o n o f t h e D P
f r o m t h e s u b s i d i a r y i n t e n t i o n s o f t h e D P . F o r e x a m p l e i n
t h e m o v i e s a r g u m e n t o f S e c t i o n 3 .1 , t h e p r i m a r y i n t e n -
t i o n i s f o r t h e r e a d e r t o c o m e t o b e l i e v e th a t p a r e n t s a n d
t e a c h e r s s h o u l d k e e p c h i l d r e n f r o m s e e i n g t o o m a n y
m o v i e s ; i n t h e t a s k d i a l o g u e o f S e c t i o n 3 . 2 , t h e i n t e n t i o n
i s t h a t th e a p p r e n t i c e r e m o v e t h e f l y w h e e l . S u b s i d i a r y
i n t e n t i o n s i n c l u d e , r e s p e c t i v e l y , t h e i n t e n t i o n t h a t t h e
r e a d e r b e l i e v e t h a t i t i s i m p o r t a n t t o e v a l u a t e m o v i e s a n d
t h e i n t e n t i o n t h a t t h e e x p e r t h e l p t h e a p p r e n t i c e l o c a t e
t h e s e c o n d s e t s c r e w .
B e c a u s e t h e b e l i e f s a n d i n t e n t i o n s o f a t l e a s t t w o
d i f f e r e n t p a r t i c i p a n t s a r e i n v o l v e d i n d i s c ou r s e , t w o p r o p -
e r t i e s o f t h e g e n e r a l - a c t i o n s i t u a t i o n ( a s s u m i n g a s i n g l e
a g e n t p e r f o r m s a ll a c t i o n s ) d o n o t c a r r y o v e r . F i r s t, i n a
d i s c o u r se , t h e I C P i n t e n d s t h e O C P t o r e c o g n i z e t h e I C P ' s
b e l i e f s a b o u t t h e c o n n e c t i o n s a m o n g v a r i o u s p r o p o s i t i o n s
a n d a c t i o n s . F o r e x a m p l e , i n t h e m o v i e s a r g u m e n t , t h e
r e a d e r ( O C P ) i s i n t e n d e d t o r e c o g n i z e t h a t t h e a u t h o r
( I C P ) b e l i e v e s s o m e p r o p o s i t i o n s p r o v i d e s u p p o r t f o r
o t h e r s ; i n t h e t a s k d i a l o g u e t h e e x p e r t ( I C P ) i n t e n d s t h e
a p p r e n t i c e ( O C P ) t o r e c o g n i z e t h a t t h e e x p e r t b e l i e v e s
t h e p e r f o r m a n c e o f c e r t a i n a c t i o n s c o n t r i b u t e s t o t h e
p e r f o r m a n c e o f o t h e r a c t i o n s . I n c o n t r a s t , i n t h e g e n e r -
a l - a c t i o n s i t u a t i o n i n w h i c h t h e r e i s n o c o m m u n i c a t i o n ,
t h e r e i s n o n e e d f o r r e c o g n i t i o n o f a n o t h e r a g e n t ' s b e l i e f s
a b o u t t h e i n t e r r e l a t i o n s h ip o f v a r i o u s a c t i o n s a n d
i n t e n t i o n s .
T h e s e c o n d d i f f e r e n c e c o n c e r n s t h e e x t e n t t o w h i c h
t h e s u b s i d i a r y a c t i o n s o r i n t e n t i o n s s p e c i f y th e o v e r a l l
a c t i o n o r i n t e n t io n . T o p e r f o r m s o m e a c t i o n , t h e a g e n t
m u s t p e r f o r m e a c h o f t h e s u b a c t i o n s i n v o lv e d ; b y
p e r f o r m i n g a ll o f t h e s e s u b a c t i o n s t h e a g e n t p e r f o r m s t h e
a c t i o n . I n c o n t r a s t i n a d i s c o u r s e , t h e p a r t i c i p a n t s s h a r e
t h e a s s u m p t i o n o f d i s c o u r s e s u f f i c i e n c y : i t i s a c o n v e n t i o n
o f t h e c o m m u n i c a t i v e s i t u a t i o n t h a t t h e I C P b e l i e v e s t h e
d i s c o u r s e i s s u f f i c ie n t t o a c h i e v e t h e p r i m a r y i n t e n t i o n o f
t h e D P . D i s c o u r s e s u f f i c i e n c y d o e s n o t e n t a i l l o g ic a l
s u f f i c i e n c y o r a c t i o n c o m p l e t e n e s s . I t i s n o t n e c e s s a r i l y
t h e c a s e t h a t s a t i s f a c t i o n o f a l l o f t h e D S P s i s s u f f i c i e n t i n
a n d o f i ts e l f f o r s a t i s f a c t i o n o f t h e D P . R a t h e r , t h e r e i s a n
a s s u m p t i o n t h a t t h e i n f o r m a t i o n c o n v e y e d i n t h e
d i s c o u r s e w i l l s u f f i c e i n c o n ju n c t i o n w i t h o t h e r i n f o r m a t i o n
t h e I C P b e l i e v es t h e O C P h a s ( o r c a n o b t a i n ) t o a l l o w f o r
s a t i s f a c t i o n o f t h e p r i m a r y i n t e n t i o n o f t h e D P . S a t i s f a c -
t i o n o f a l l o f t h e D S P s , i n c o n j u n c t i o n w i t h t h i s a d d i t i o n a l
i n f o r m a t i o n , is e n o u g h f o r s a t i s fa c t i o n o f t h e D P . H e n c e ,
i n d is c o u r s e t h e i n t e n t i o n a l s t r u c t u r e ( t h e a n a l o g u e o f t h e
a c t i o n h i e r a r c h y ) n e e d n o t b e c o m p l e t e .
F o r e x a m p l e , t h e p r o p o s i t i o n s e x p r e s s e d i n t h e m o v i e s
e s s a y d o n o t p r o v i d e a l o g i c a ll y s u f f i c i e n t p r o o f o f t h e
c l a i m . T h e a u t h o r f u r n i s h e s i n f o r m a t i o n h e b e l i e v e s t o b e
a d e q u a t e f o r t h e r e a d e r t o r e a c h t h e d e s i r e d c o n c l u s i o n
a n d a s s u m e s t h e r e a d e r w i l l s u p p l e m e n t w h a t i s a c t u a l l y
s a i d w i t h a p p r o p r i a t e a d d i t i o n a l i n f o r m a t i o n a n d r e a s o n -
i n g. L i k e w i s e , t h e t a s k d i a lo g u e d o e s n o t m e n t i o n a l l t h e
s u b t a s k s e x pl i ci t ly . I n s t e a d , t h e e x p e r t a n d a p p r e n t i c e
d i s c us s e x p l i c it l y o n l y t h o s e s u b t a s k s f o r w h i c h s o m e
i n s t r u c t i o n i s n e e d e d o r i n c o n n e c t i o n w i t h w h i c h s o m e
p r o b l e m a r i se s .
T o b e m o r e c o n c r e t e , w e s h a l l l o o k a t t h e e x t e n s i o n o f
t h e G r i c e a n a n a l y s i s f o r t w o p a r t i c u l a r c a s e s , o n e i n v o l v -
i n g a b e l i e f , t h e o t h e r a n i n t e n t i o n t o p e r f o r m s o m e
a c t i o n . W e s h a ll c o n s i d e r o n l y t h e s i m p l e s t s i t u a t io n s , i n
w h i c h t h e p r i m a r y in t e n ti o n s o f t h e D P / D S P s a r e a b o u t
e i t h e r b e l ie f s o r a c t i o n s , b u t n o t a m i x t u r e . A l t h o u g h t h e
t a s k d i a l o g u e o b v i o u s l y i n v o l v e s a m i x t u r e , t h i s i s a n
e x t r e m e l y c o m p l i c a t e d i s s ue t h a t d e m a n d s a d d i ti o n a l
r e s e a r c h .
7.2 THE BELIEF CASE
I n t h e b e l i e f c a s e , th e p r i m a r y i n t e n t i o n o f t h e D P i s t o
g e t t h e O C P t o b e l i e v e s o m e p r o p o s i t i o n , s a y p . E a c h o f
t h e d i s c o u r s e s e g m e n t s i s a l s o i n t e n d e d t o g e t t h e O C P t o
b e l i e v e a p r o p o s i t i o n , s a y q i f o r s o m e i = 1 . . . . n ( w h e r e
t h e r e a r e n d i sc o u r s e s e g m e n t s ) . I n a d d i t io n t o t h e p r i m a -
r y i n t e n t i o n - i . e ., t h a t t he O C P s h o u l d c o m e t o b e l i e v e p
t h e D P in c l u d e s a n i n t e n t i o n t h a t t h e O C P c o m e t o
b e l i e v e e a c h o f t h e q i a n d , i n a d d i t i o n , a n i n t e n t i o n t h a t
t h e O C P c o m e t o b e l i e v e t h e q i p r o v i d e s u p p o r t f o r p . W e
c a n r e p r e s e n t t h i s s c h e m a t i c a l l y a s : 19
Y i = 1 . . .. n I n t e n d ( I C P , B e l i e v e ( O C P , p ) A
B e l i e v e ( O C P , q i ) A
B e l i e ve ( O C P , S u p p o r t s ( p , q l A . . . A q n ) ) )
T h e r e a r e s e v e r a l t hi n g s to n o t e h e r e . T o b e g i n w i t h,
t h e f i r s t i n t e n t io n , ( I n t e n d I C P ( B e l i e v e ( O C P p ) ) , i s th e
p r i m a r y c o m p o n e n t o f t h e DS P . S e c o n d , e a c h o f t h e
20 0 Computational Linguistics, Volume 12, Number 3, July-Sept ember 1986
B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
i n t e n d e d b e l i e fs in th e s e c o n d c o n j u n c t c o r r e s p o n d s t o
t h e p r i m a r y c o m p o n e n t o f t h e D S P o f s o m e e m b e d d e d
d i s c o u r se s e g m e n t . T h i r d , t h e
supports
r e l a t i o n i s n o t
i m p l i ca t i o n. T h e O C P i s n o t i n t e n d e d t o b e l i e v e t h a t t h e
q i i m p l y p , b u t r a t h e r t o b e l i e v e t h a t t h e q i i n c o n j u n c t i o n
w i t h o t h e r f a c t s a n d r u l e s t h a t t h e I C P a s s u m e s t h e O C P
h a s a v a i l a b l e o r c a n o b t a i n a n d t h u s c o m e t o b e l i e v e a r e
s u f f i c i e n t f o r t h e O C P t o c o n c l u d e p . F o u r t h , t h e
D P / D S P m a y o n l y b e c o m p l e t e l y d e t e r m i n e d a t t h e e n d
o f t h e d i s c o u r s e ( s e g m e n t ) , a s w e d i s c u s s e d i n S e c t i o n 4 .
F i n a l l y , t o d e t e r m i n e h o w t h e d i s c o u r s e s e g m e n t s
c o r r e s p o n d i n g t o t h e q i a r e r e l a t e d t o t h e o n e c o r r e -
s p o n d i n g t o p , t h e O C P o n l y h a s t o b e l i e v e t h a t t h e I C P
b e l i e v e s a s u p p o r t s r e l a t i o n s h ip h o ld s . H e n c e , f o r t h e
p u r p o s e o f r e c o g n i z i n g t h e d i s c o u r s e s t r u c t u r e , i t w o u l d
b e s u f f i c i e n t f o r t h e t h i r d c l a u s e t o b e
. . . B e l i e v e ( O C P , B e l i e v e ( I C P ,
S u p p o r ts ( p , q l A . . .A q n ) ) )
H o w e v e r , t h e D P o f a b e l i e f - c a s e d i s c o u r s e i s n o t m e r e l y
t o g e t t h e O C P t o b e l i e v e p , b u t t o g e t t h e O C P t o b e l i e v e
p b y v i r t u e o f b e l i e v i n g t h e q i . T h a t t h i s i s s o c a n b e s e e n
c l e a r l y b y c o n s i d e r i n g s i t u a t i o n s i n w h i c h t h e O C P
a l r e a d y b e l i e v e s p a n d i s k n o w n b y t h e I C P t o d o s o , b u t
d o e s n o t h a v e a g o o d r e a s o n f o r b e l i e v i n g p . T h i s l a s t
p r o p e r t y o f t h e b e l i e f c a s e i s n o t s h a r e d b y t h e a c t i o n
c a s e .
T h e r e i s a n i m p o r t a n t r e l a t i o n s h i p b e t w e e n t h e
s u p p o r t s r e l a t i o n a n d t h e d o m i n a n c e r e l a t i o n t h a t c a n
h o l d b e t w e e n D P / D S P s ; i t i s c a p t u r e d i n t h e f o l lo w i n g
r u le ( u s i n g th e s a m e n o t a t i o n a s a b o v e ) :
¥ i = 1 . . .. n I n t e n d ( C P 1, B e l i e v e ( C P 2 , p ) ) A
I n t e n d ( C P p B e l i e v e ( C P 2 , q i ) ) A
B e l i e v e ( C P p S up p o r t s( p , q l A . . . A q n ) ) ~
D O M ( I n t e n d ( C P p B e l ie v e (C P 2 ,p ) )
I n t e n d ( C P 1 , B e l i e v e ( C P 2 , q i ) ) )
T h e i m p l i c a t io n i n t he f o r w a r d d i r e c t i o n s t a t e s t h a t i f a
c o n v e r s a t i o n a l p a r t i c i p a n t ( C P I ) b e l i e v e s t h a t t h e p r o p o -
s i t i o n p i s s u p p o r t e d b y t h e p r o p o s i t i o n q i , a n d h e i n t e n d s
a n o t h e r p a r t i c i p a n t ( C P 2 ) t o a d o p t t h e s e b e l i e f s , t h e n h i s
i n t e n t i o n t h a t CP 2 b e l i e v e p d o m i n a t e s h i s i n t e n t io n t h a t
C P 2 b e l i e v e q i- V i e w e d i n t u i t iv e l y , C P l ' s b e l i e f t h a t q i
p r o v i d e s s u p p o r t f o r p , u n d e r l i e s h i s i n t e n t i o n t o g e t CP 2
t o b e l i e v e p b y g e t t i n g h i m t o b e l i e v e q i . T h e s a t i s f a c t i o n
o f C P ~ ' s i n t e n t i o n t h a t C P 2 s h o u l d b e l i e v e q i w il l h e l p
s a t i s f y C P ~ ' s i n t e n t i o n t h a t
CP 2
b e l i e v e p . T h i s r e l a t i o n -
s h i p p l a y s a r o l e i n t h e r e c o g n i t i o n o f D S P s.
7.3 THE ACTION CASE
A n a n a l o g o u s s i t u a t i o n h o l d s f o r a d i s c o u r s e s e g m e n t
c o m p r i s i n g u t t e r a n c e s i n t e n d e d t o g e t t h e O C P t o
p e r f o r m s o m e s e t o f a c t i o n s d i r e c t e d a t a c h i e v i n g s o m e
o v e r a l l t a s k ( e . g ., s o m e s e g m e n t s i n th e t a s k - o r i e n t e d
d i a l o g u e o f S e c t i o n 3 . 2 ) . T h e f u l l s p e c i f i c a t i o n o f t h e
D P / D S P c o n t a i n s a
generates
r e l a t i o n t h a t i s d e r i v e d f r o m
a r e l a t i o n d e f i n e d b y G o l d m a n ( 1 9 7 0 ) . F o r t h i s c a s e , t h e
D P / D S P s a r e o f t h e f o l l o w i n g f o r m :
¥ i = 1 . . .. n I n t e n d ( IC P , I n t e n d ( O C P , D o ( A ) ) A
I n t e n d ( O C P , D o ( a i ) ) A
B e l i e v e ( O C P , B e l i e v e ( I C P ,
G e n e r a t e s ( A , a l A . . . A a n ) ) ) )
E a c h i n t e n t i o n t o a c t r e p r e s e n t e d i n t h e s e c o n d c o n j u n c t
c o r r e s p o n d s t o t h e p r i m a r y i n t e n t i o n o f s o m e d i s c o u r s e
s e g m e n t .
L i k e s u p p o r t s , t h e g e n e r a t e s r e l a t i o n i s p a r t i a l ( i t s
p a r t i a l i t y d i s t i n g u i s h e s i t i n p a r t f r o m G o l d m a n ' s
r e l a t i o n ) . T h u s , t h e O C P i s n o t i n t e n d e d t o b e l i e v e t h a t
t h e I C P b e l i e v e s t h a t p e r f o r m a n c e o f a i a l o n e i s s u ff i c i e n t
f o r p e r f o r m a n c e o f A , b u t r a t h e r t h a t d o i n g a ll o f t h e a i
a n d o t h e r a c t i o n s t h a t t h e O C P c a n b e e x p e c t e d t o k n o w
o r fi g u r e o u t c o n s t i t u t e s a p e r f o r m a n c e o f A . I n th e t a s k
d i a l o g u e o f S e c t i o n 3 .2 , m a n y a c t i o n s t h a t a r e e s s e n t i a l t o
t h e t a s k ( e . g . , t h e a p p r e n t i c e p i c k i n g u p t h e A l l e n w r e n c h
a n d a p p l y i n g i t c o r r e c t l y t o t h e s e t s c r e w s ) a r e n e v e r e v e n
m e n t i o n e d i n t he d i a l o g u e .
N o t e t h a t i t i s u n n e c e s s a r y f o r t h e I C P o r O C P t o h a v e
a c o m p l e t e p l a n r ~ l a t i n g a l l o f t h e a i t o A a t t h e s t a r t o f
t h e d i s c o u r s e ( o r d i s c o u r s e s e g m e n t ) . A l l th a t i s r e q u i r e d
i s t h a t , f o r a n y g i v e n s e g m e n t , t h e O C P b e a b l e t o d e t e r -
m i n e w h a t i n t e n t io n t o a c t t h e s e g m e n t c o r r e s p o n d s t o
a n d w h i c h o t h e r i n t e n t i o n s d o m i n a t e t h a t i n t e n t i o n .
F i n a l ly , u n l ik e t h e b e l i e f c a s e , th e t h i r d c o n j u n c t h e r e
r e q u i r e s o n l y t h a t t h e O C P r e c o g n i z e t h a t t h e I C P
b e l i e v e s a g e n e r a t e s r e l a t i o n s h i p h o l d s . T h e O C P c a n d o
A b y v i r t u e o f d o i n g t h e a i w i t h o u t c o m i n g h i m s e l f t o
b e l i e v e a n y t h i n g a b o u t t h e r e l a ti o n s h i p s b e t w e e n A a n d
the a i .
A s i n t h e b e l i e f c a s e , t h e r e i s a n e q u i v a l e n c e t h a t l i n k s
t h e g e n e r a t e s r e l a t i o n a m o n g a c t i o n s t o t h e d o m i n a n c e
r e l a t i o n b e t w e e n i n t e n t i o n s . S c h e m a t i c a l l y , i t i s a s
f o l l o w s :
¥ i = 1 . . . . n I n t e n d ( C P 1, I n t e n d ( C P 2, D o ( A ) ) ) A
I n t e n d ( C P 1 , I n t e n d ( C P 2 , D o ( a i ) ) ) A
B e l i e v e ( C P t , G e n e r a t e s ( A , a l A . . . A a n ) ) < >
D O M ( I n t e n d (C P 1 , I n te n d (C P 2 , D o ( A ) ) )
I n t e n d ( C P t, I n t e n d ( C P 2, D o ( a i ) ) ) )
T h i s e q u i v a l e n c e s t a t e s t h a t , i f a n a g e n t ( C P 1) b e l i e v e s
t h a t t h e p e r f o r m a n c e o f s o m e a c t i o n ( a i ) c o n t r i b u t e s i n
p a r t t o t h e p e r f o r m a n c e o f a n o t h e r a c t i o n ( A ) , a n d i f C P 1
i n t e n d s f o r
CP 2 to
( i n t e n d t o ) d o b o t h o f t h e s e a c t i o n s ,
t h e n h i s i n t e n t i o n t h a t C P 2 ( i n t e n d t o ) p e r f o r m a i is
d o m i n a t e d b y h is i n te n t i o n t h a t CP 2 ( i n t e n d t o ) p e r f o r m
A . V i e w e d i n t u i t i v e l y , C P 1 ' s b e l i e f t h a t d o i n g a i w i l l
c o n t r i b u t e t o d o i n g A u n d e r l i e s h i s i n t e n t i o n t o g e t
CP 2
t o d o A b y g e t t i n g CP 2 to d o a i. T h e s a t i s f a c t i o n o f C P t ' s
i n t e n t i o n f o r C P 2 t o d o a i w i l l h e l p s a t i s f y C P ~ ' s i n t e n t i o n
f o r
CP 2 to
d o A .
S o , f o r e x a m p l e , i n t h e t a s k - o r i e n t e d d i a l o g u e o f
S e c t i o n 3 . 2 , t h e e x p e r t k n o w s t h a t u s i n g t h e w h e e l p u l l e r
i s a n e c e s s a r y p a r t o f r e m o v i n g t h e f l y w h e e l . H i s i n t e n -
t i o n t h a t t h e a p p r e n t i c e i n t e n d t o u s e t h e w h e e l p u U e r i s
t h u s d o m i n a t e d b y h i s i n t e n t i o n t h a t t h e a p p r e n t i c e
i n t e n d t o t a k e o f f t h e f l y w h e e l . S a t i s f a c t i o n o f t h e i n t e n -
t i o n t o u s e t h e w h e e l p u l l e r w i l l c o n t r i b u t e t o s a t i s f y i n g
C o m p u t a t i o n a l L i n g u i s t i c s , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r 1986 201
B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t io n s , a n d t h e S t r u c t u r e o f D i s c o u r s e
Reichm an-Adar, R. 1984 Extende d Person-Ma chine Interface.
Ar t i f i -
c ia l In t e l l i gence 22(2): 157-218.
Reinhart, T. 1981 Pragmatics and Linguistics: An Analysis of Sentence
Topics. Phi losoph i ca 27( 1 :53-94.
Robins on, A. 1981 Determi ning Verb Phrase Referents in Dialogs.
A m e r i c a n J o u r n a l o f C o m p u t a t i o na l L i n g u is t i c s 7 ( 1 ) : 1 - 1 6 .