ref.erence identification errors... [J switches to SLIDEVALVE] J... Base is blue... take the big blue 3... It's kind of blue." Second.. Thls type of negotiation, called self-negotlatlon.
Trang 1BY RELAXATION
B r a d l e y A G o o d m a n
B B N Laboratories I0 M o u l t o n Street
C a m b r i d g e Mass 0 2 2 3 8
ABSTRACT
T h e goal of thls w o r k is the e n r i c h m e n t of
h u m a n - m a c h l n e m t e r a c t I o n s in a natural l a n g u a g e
envlronment 1 W e w a n t to provide a f r a m e w o r k less
restrictive t h a n earlier o n e s b y allowing a s p e a k e r
leeway tn forming a n u t t e r a n c e a b o u t a task a n d in
determining the conversational vehicle to deliver it, A
s p e a k e r a n d listener c a n n o t be a s s u r e d to h a v e the
s a m e beliefs, contexts, b a c k g r o u n d s or goals at e a c h
point in a conversation As a result, dlfflcultles a n d
mistakes arise w h e n a listener interprets a s p e a k e r s
utterance T h e s e mistakes c a n lead to various kinds of
m l s u n d e r s t a n d l n g s b e t w e e n s p e a k e r a n d hstener
including reference failures or failure to u n d e r s t a n d
m t s u n d e r s t a n d l n g s m l s c o m m u n m a t l o n S u c h m~stakes
constitute a klnd of "ill-formed" input that c a n slow
d o w n e n d possibly b r e a k d o w n c o m m u n i c a t i o n O u r goal
~s to recognize a n d Isolate s u c h m l s c o m m u n l c a t t o n s a n d
c i r c u m v e n t them Thls p a p e r will h l g h h g h t a particular
class of m l s c o m m u n l c a t l o n - reference p r o b l e m s - by
d e s c r l b m g a case study, includlng t e c h n i q u e s for
avoldlng failures of r e f e r e n c e
I Introduction
Cohen, Perrault a n d Allen s h o w e d in thelr p a p e r
" B e y o n d Question A n s w e r i n g " [8~ that ", users of
cluestlon-answerzng s y s t e m s expect t h e m to do m o r e
t h a n just a n s w e r isolated questions - - they expect
s y s t e m s to e n g a g e tn conversation In doing ~o, the
s y s t e m ts e x p e c t e d to allow users to be less than
meticulously hteral ~n c o n v e y i n g their zntentlons, a n d tt
is e x p e c t e d to m a k e hnguxstlc a n d p r a g m a t i c use of the
previous discourse." Following in thelr footsteps, w e
w a n t to build robust natural l a n g u a g e processing
s y s t e m s that c a n detect a n d recover from
m l s c ~ m m u n l c a t t o n T h e d e v e l o p m e n t of s u c h systems
requires s study o n h o w people c o m m u n i c a t e a n d h o w
they recover from p r o b l e m s In c o m m u n i c a t i o n This
p a p e r s u m m a r i z e s the results of a dissertation [13]
that tnvestlgates the kinds of m l s c o m m u n l c a t l o n that
o c c u r in h u m a n c o m m u n i c a t i o n with a special e m p h a s i s
o n reference prooiems, i.e p r o b l e m s a listener has
determining w h o m or w h a t a s p e a k e r ts talking about
W e h a v e written c o m p u t e r p r o g r a m s a n d algorithms that
d e m o n s t r a t e h ~ w o n e could h a n d l e s u c h p r o b l e m s m
C - ~ 3 7 8
the c o n t e x t of a natural l a n g u a g e u n d e r s t a n d 2 n g system T h e s t u d y of m z s c o m m u n l c a t l o n is a n e c e s s a r y task w l t h m s u c h a c o n t e x t since a n y c o m p u t e r capable
of c o m m u n l c a t ~ n g with h u m a n s tn natural l a n g u a g e m u s t
be tolerant of the tmprecIse, lll-devlsed or c o m p l e x
u t t e r a n c e s that people often use
O u r c u r r e n t r e s e a r c h [25, 26] views m o s t dialogues as being cooperatlve a n d goal directed, l,e a
s p e a k e r a n d h s t e n e r w o r k together to achieve a
c o m m o n goal T h e interpretation of a n u t t e r a n c e involves Identifying the underlying plan or goal that the u t t e r a n c e reflects [5 I, 2 3 ] Thls plan, however, is rarely, d ever, obvious at the surface s e n t e n c e level
A central issue In the interpretation of u t t e r a n c e s ts the t r a n s f o r m a t i o n of s e q u e n c e s of imprecise, zll- devised or c o m p l e x u t t e r a n c e s into w e l l - s p e c l h e d plans that might b e carried out b y dialogue participants Within thls context, m l s c o m m u n l c a t l o n c a n occur
W e ere particularly c o n c e r n e d with cases of
m x s c o m m u n l c a t l o n from the heater's viewpoint, s u c h as
w h e n the h e a r e r is m a t t e n t l v e to c o n f u s e d about, or
ordinary e x c h a n g e s s p e a k e r s usually m a k e a s s u m p t i o n s regarding w h a t thelr listeners k n o w a b o u t a topic of discussion T h e y w111 leave out details t h o u g h t to be superfluous [2 19] Since the s p e a k e r really does not
k n o w exactly w h a t a listener k n o w s a b o u t a topic, tt ts easy to m a k e s t a t e m e n t s that c a n b e misinterpreted or
not u n d e r s t o o d b y the listener b e c a u s e not e n o u g h
details w e r e presented O n e principal s o u r c e of trouble
Is the description c o n s t r u c t e d b y the s p e a k e r to refer
to a n actual object in the world T h e d e s c m p t l o n c a n
be tmpreclse, confused, a m b i g u o u s or over!v speclflc It might be interpreted u n d e r the w r o n g context This leads to dlfflculty for the h s t e n e r w h e n figuring out
w h a t oblect ~s being described, that Is ref.erence identification errors S u c h descriptions are "all-
f o r m e d " input, the b l a m e for ill-formedness m a y lie partly with the s p e a k e r a n d partly with the listener
T h e s p e a k e r m a y h a v e b e e n sloppy or not t a k e n the
h e a r e r into consideration, the listener m a y be either remiss or unwilling to admit h e can't u n d e r s t a n d the
s p e a k e r a n d to ask the s p e a k e r for clarification, or
m a y slmply feel that he h a s u n d e r s t o o d w h e n he zn fact has not
Thls w o r k ts part of a n o n - g o i n g e f f o r t to develop a reference Identlfzcatmn a n d plan recognition
m e c h a n i s m that c a n exhibit m o r e " h u m a n - h k e ' tolerance of s u c h utterances O u r goal zs to build a
m o r e robust s y s t e m that c a n handle errorful utterances, a n d ~hat c a n be i n c o r p o r a t e d in exlstlng systems As a start, w e h a v e c o n c e n t r a t e d o n
imperfect descriptions to c o m m u n i c a t e a b o u t objects;
s o m e t i m e s their p a r t n e r s s u c c e e d zn u n d e r s t a n d i n g a n d occasionally they fail A n y c o m p u t e r h o p i n g to play the part of a listener m u s t b e c a p a b l e of taking w h a t the
204
Trang 2it W e are developing a t h e o r y of the use of
extensional descrlptlons that will help e x p l a m h o w
people successfully use s u c h imperfect descriptions
W e call thls the theory of reference m l s c o m m u n l c a t i o n
Section 2 of this p a p e r highlights s o m e aspects of
n o r m a l c o m m u n i c a t i o n a n d t h e n provides a general
discussion o n the types of m i s c o m m u n l c a t l o n that o c c u r
In conversation, concentrating primarily o n reference
p r o b l e m s a n d motivating m a n y of t h e m with Illustrative
protocols Section 3 presents possible w a y s a r o u n d
s o m e of the p r o b l e m s of m i s c o m m u n x c a t i o n in reference
reference m e c h a n i s m that attempts to o v e r c o m e m a n y
reference problems
W e are following the t a s k - o m e n t e d p a r a d i g m of
G r o s z [ 1 4 ] s i n c e i t Is e a s y t o s t u d y ( t h r o u g h
v i d e o t a p e s ) It p l a c e s t h e w o r l d In f r o n t o f y o u ( a
p r i m a r i l y e x t e n s i o n a l w o r l d ) , a n d It l i m i t s t h e
d l s c u s s l o n w h l l e s t i l l p r o v i d i n g a r l c h e n v i r o n m e n t f o r
c o m p l e x d e s c r i p t i o n s T h e t a s k c h o s e n a s t h e t a r g e t
f o r t h e s y s t e m Is t h e a s s e m b l y o f a t o y w a t e r p u m p
T h e w a t e r p u m p Is r e a s o n a b l y c o m p l e x , c o n t a i n i n g f o u r
s u b a s s e m b l i e s t h a t a r e b u i l t f r o m p l a s t i c t u b e s ,
n o z z l e s , v a l v e s , p l u n g e r s , a n d c a p s t h a t c a n b e s c r e w e d
o r p u s h e d t o g e t h e r A l a r g e c o r p u s o f d i a l o g u e s
c o n c e r n i n g t h l s t a s k w a s c o l l e c t e d b y C o h e n ( s e e
[7 8 9 ] ) T h e s e d i a l o g u e s c o n t a i n e d i n s t r u c t i o n s f r o m
a n " e x p e r t " t o a n " a p p r e n t i c e " t h a t e x p l a i n t h e
assembly of the toy water p u m p , Both participants
w e r e w o r k i n g t o a c h i e v e a c o m m o n g o a l - t h e
s u c c e s s f u l a s s e m b l y of t h e p u m p T h l s d o m a i n Is r l c h
m p e r c e p t u a l i n f o r m a t i o n , a l l o w i n g f o r c o m p l e x
d e s c r i p t i o n s of e l e m e n t s i n it T h e d a t a p r o v i d e
e x a m p l e s of imprecision, confusion, a n d ambiguity as
we!l as attempts to correct these p r o b l e m s
T h e following e x c h a n g e exemplifies o n e s u c h
situation Here A Is instructing J to a s s e m b l e part o f
t h e w a t e r pump R e f e r t o F i g u r e l ( a ) f o r a p i c t u r e of
t h e p u m p A a n d J a r e c o m m u n i c a t i n g v e r b a l l y b u t
n e i t h e r c a n s e e t h e o t h e r ( T h e b r a c k e t e d t e x t In t h e
e x c e r p t t e l l s w h a t w a s a c t u a l l y o c c u r r i n g w h i l e e a c h
u t t e r a n c e w a s s p o k e n ) N o t l c e t h e c o m p l e x i t y o f t h e
s p e a k e r ' s d e s c r i p t i o n s a n d t h e r e s u l t a n t p r o c e s s i n g
r e q u i r e d b y t h e l i s t e n e r , T h l s d i a l o g u e i l l u s t r a t e s w h e n
l i s t e n e r s r e p a i r t h e s p e a k e r s d e s c r i p t i o n in o r d e r t o
f l n d a r e f e r e n t , w h e n t h e y r e p a i r t h e i r m z t l a l r e f e r e n c e
c h o i c e o n c e t h e y a r e g i v e n m o r e i n f o r m a t i o n , a n d w h e n
t h e y f a l l t ~ c h o o s e a p r o p e r r e f e r e n t In Linp 7, A
:[,=scribes the two holes on the BAjEVALVE as "the httle
h o i e " J m u s t r e p a i r t h e d e s c r l p t l o n , r e a h z m g that A
d o e s n t r e a l l y m e a n " o n e h o l e b u t is r e f e r r i n g t o t,~e
' t w o ' h o l e s J a p p a r e n t l y d o e s t h i s s i n c e h e d o e s n t
c o m p l a i n a b o u t a s d e s c r i p t i o n a n d c o r r e c t l y a t t a c h e s
the B A S E V A L V E to the T U B E B A S E F i g u r e l i b ) s h o w s
the c o n f i g u r a t i o n of the p u m p a f t e r the T U B E B A S E is
a t t a c h e d t o t h e M A I N T U B E "n L m e I 0 , [n L m e 13 J
i n t e r p r e t s " a r e d p l a s t i c p i e c e " t o r e f e r t o t h e V O Z Z L E
W h e n A a d d s t h e r e l a t i v e c l a u s e " t h a t h a s f o u r g i = m o s
on it." J is forced to drop the N O Z Z L E as the r e f e r e n t
a n d to se{ect the S L L D E V ~ L V E In L m e s i7 a n d 18, A'S
description "the o t h e r - - t h e o p e n part o f the maln
tube the lower valve" is ambiguous, a n d J selects the
w r o n g s l t e , n a m e l y t h e TUBEBAEE, in w h i c h t o i n s e r t
d e t e c t a n y trouble L~nes 20 a n d 21 k e e p I f r o m
t h i n k i n g t h a t s o m e t h i n g is w r o n g b e c a u s e t h e p a r t f i t s
l o o s e l y , In L~nes 27 a n d 2 8 , J i n d i c a t e s t h a t A d l d n o t
g l v e him e n o u g h z n f o r m a t l o n to perform the requested
a c t i o n In L m e 3 0 J f u r t h e r c o m p o u n d s t h e e r r o r i n
Line 18 b y putting t h e S P O U T on t h e TUBEBASE
E x c e r p t 1 ( T e l e p h o n e )
[J g r a b s t h e T U B E B A S E ]
2 t h a t h a s t w o l i t t l e t e e t h s t i c k i n g
3 o u t o f t h e b o t t o m o f it
J: 4 Y e a h
A 5 O k a y O n that take the
6 brlght shocking pink piece of plastic [J takes B A S E V A L V E ]
7 a n d stick the little hole over the
t e e t h
[J s t a r t s to i n s t a l l t h e BASEVALVE b a c k s off, l o o k s
at it a g a i n a n d t h e n g o e s a h e a d a n d
i n s t a l l s it]
J 8 O k a y
A: 9 N o w s c r e w t h a t b l u e c a p o n t o
I 0 t h e b o t t o m o f t h e m a l n t u b e [J screws TUBEBASE onto M A I N T U B E ]
J 11 O k a y
A 12 Now t h e r e ' s a - -
13 a r e d p l a s t i c p i e c e [J starts for N O Z Z L E ]
1 4 t h a t h a s f o u r g i z m o s o n It
[J switches to SLIDEVALVE]
J 1 5 Yes
A 16 O k a y Put the u n g t z m o e d e n d In the
u h
1 7 the o t h e r - - t h e open
1 8 p a r t o f t h e m a l n t u b e , t h e l o w e r
v a l v e [3 p u t s SLIDEVALVE i n t o h o l e i n TUBEBASE, b u t A
I 19 All r i g h t
A 20 !t ;ust hts loosely It doesnt '~I have to f'.t right Okay then take .~2 the clear plastic elbow ]omt [J takes S P O U T ]
J 23 All r i g h t
A $4 A n d put tt over the bottom opening, too
[J trees installing S P O U T o n TI/BEBASE]
l -~ O k a y
a 28 O k a y Now t a k e t h e - -
2 7 W h i c h e n d a m I s u p p o s e d to p u t It over')
28 Do y o u k n o w °
A -:'9 Put t h e - - p u t t h e - - t h e big e n d - -
3 0 the blg e n d over it
[J p u s h e s big e n d of S P O U T o n T U B E B A S E twlstlng
zt to f o r c e it on]
205
Trang 3NO:zZe
Figure I:
I,~.d)
I'
T h e T o y W a t e r P u m p
C
2 M i s c o m m u n i c a t i o n
People m u s t a n d d o m a n a g e to resolve lots of
(potentaal) m a s c o m m u m c a t a o n In e v e r y d a y conversataon
M u c h of it as resolved s u b c o n s c a o u s l y wlth the
h s t e n e r u n a w a r e that a n y t h i n g is wrong, O t h e r
m l s c o m m u m c a t l o n is resolved wath the listener actively
deleting or replacang m f o r m a t a o n m the s p e a k e r s
utterance until It flts the c u r r e n t context S o m e t i m e s
thls resolutlon Is p o s t p o n e d until the questlonable part
of the utterance is actually needed S h l l w h e n all
these fail the h s t e n e r c a n ask the s p e a k e r to clarlfy
w h a t w a s said 2
T h e r e are m a n y aspects of a n utterance that the
h s t e n e r c a n b e c o m e c o n f u s e d a b o u t a n d that c a n lead
to m a s c o m m u n a c a t t o n T h e h s t e n e r c a n b e c o m e
c o n f u s e d a b o u t w h a t the s p e a k e r intends for the
referents, the actaons, a n d the goals described b y the
utterance, Confuslons often a p p e a r to result from
confhct b e t w e e n the c u r r e n t state of the conversation
the overall goal of the speaker, or the m a n n e r In w h i c h
the s p e a k e r p r e s e n t e d the anformatlon H o w e v e r , w h e n
the h s t e n e r steps b a c k a n d is able to discover w h a t
k~nd of confuslon ~s occurring, t h e n the confusion c a n
qulte possibly be resolved
2.1 C a u s e s of m l s c o m m u n i c a t i o n
Thls sectaon attempts to motlvate a p a r a d l g m for
the kinds of conversation that w e studled a n d traes to
point out places m the p a r a d l g m that leave r o o m for
m l s c o m m u m c a t l o n
d i a l o g u e s
T a s k - o r i e n t e d c o n v e r s a t l o n s h a v e a speclfic goal
to b e achleved: the p e r f o r m a n c e of a task (e.g [14])
T h e partlclpants in the dlalogue c a n h a v e the s a m e skill level a n d they c a n slmply w o r k t o g e t h e r to
a c c o m p l i s h the task; or o n e of them, the expert, could
k n o w m o r e a n d could direct the other, the apprentlce
to p e r f o r m the task W e h a v e c o n c e n t r a t e d prlmarlly
e x a m l n e d - but m a n y of o u r observations c a n b e
g e n e r a h z e d to the f o r m e r case, too W e will refer to thls as the a p p r e n t l c e - e x p e r t domaln
T h e v l e w p o m t s of the expert a n d a p p r e n t l c e differ greatly In a p p r e n t l c e - e x p e r t e x c h a n g e s T h e expert, having a n u n d e r s t a n d l n g of the f u n c t l o n a h t y of the
e l e m e n t s in the task h a s m o r e of a feel for h o w the
e l e m e n t s w o r k together, h o w they go together, a n d h o w the indlvldual e l e m e n t s c a n b e used T h e a p p r e n t l c e
n o r m a l l y h a s n o s u c h k n o w l e d g e a n d m u s t b a s e hls declslons o n p e r c e p t u a l features s u c h as s h a p e [15]
T h e structure of the task affects the structure of the dlalogue [14} partlcularly t h r o u g h the c e n t e r of attentlon of the e x p e r t a n d apprentlce Thls is the
p h e n o m e n o n called focus [14 20 24] whlch, in t a s k - orlented dlalogues Is a very real a n d operational thlng (e.g., focus is u s e d In resolving a n a p h o r a c references) Shafts ~n focus c o r r e s p o n d dlrectly to the task, ats subtasks, the oblects an a task a n d the s u b p l e c e s of
e a c h object F o c u s a n d focus shifts are g o v e r n e d b y
m a n y rules [14 :~0, 24] C o n f u s a o n m a y result w h e n
e x p e c t e d shafts d o not take place For example If the expert c h a n g e s focus to a n object but n e v e r discusses Its s u b p a e c e s ~such as a n obvaous a t t a c h m e n t surface)
or n e v e r b o t h e r s to talk a b o u t the object r e a s o n a b l y
s o o n after its antroductlon (Le., b e t w e e n the tame of ~ts
m t r o d u c t l o n a n d its use without digressing in a well-
s t r u c t u r e d w a y In b e t w e e n (see [20])), t h e n the
a p p r e n t l c e m a y b e c o m e confused, leavang hlm r~pe for
m l s c o m m u n l c a t l o n T h e reverse anfluence b e t w e e n focus
a n d oblects c a n lead to trouble, too A shzft In focus
b y the expert that d o e s not h a v e a m a n H e s t a t l o n In the apprentlce's world wall also perplex the a p p r e n t i c e
F o c u s also influences h o w descr:ptlons are
f o r m e d [15, 2] T h e level of detail requlred in a description d e p e n d s directly o n the e l e m e n t s currently highlighted b y the f o c u s If the oblect to be descrabed
Is samflar to other e l e m e n t ~ m focus, the expert m u s t
be m o r e speclhc m the formulation of the descraptlon
or m a y conslder shlftmg focus a w a y from the posslbly
a m b i g u o u s objects to o n e w h e r e the amblgulty w o n t occur
2.2 C o n s e q u e n c e s of m i s c o m m u n i c a t l o n
In thls section we will make It clear t h a t people
d o m : s c o m m u n l c a t e a n d yet they often m a n a g e to flx
m l s c o m m u n l c a t l o n a n d descrlbe w a y s to detect them
We will h z g h h g h t relatlonsh;ps between different
m l s c o m m u n z c a t ; o n p r o b l e m s but won't necessarzly
d e m o n s t r a t e w a y s to resolve e a c h of them
2An analysis of c l a r i f i c a t i o n suodialogues can be found
;n [ 1 7 )
206
Trang 4T h e r e a r e m a n y w a y s h e a r e r s c a n g e t c o n f u s e d
d u r i n g a c o n v e r s a t i o n F i g u r e 2 o u t l i n e s s o m e of t h e m
t h a t w e r e d e r i v e d f r o m a n a l y z i n g t h e w a t e r p u m p
p r o t o c o l s T h i s s e c t i o n d e f i n e s a n d i l l u s t r a t e s m a n y of
t h e m t h r o u g h n u m e r o u s e x c e r p t s E a c h e x c e r p t i s
m a r k e d i n p a r e n t h e s e s t o s h o w w h a t m o d a l i t y of
c o m m u n i c a t i o n w a s u s e d ( s e e [9] f o r a d e s c r i p t i o n
a b o u t t h e c o l l e c t i o n of t h e s e e x c e r p t s ) E a c h
b r a c k e t e d p o r t i o n of t h e e x c e r p t e x p l a i n s w h a t w a s
o c c u r r i n g a t t h a t p o i n t i n t h e d i a l o g u e T h e c o n f u s i o n s
t h e m s e l v e s , c o u p l e d w i t h t h e d e s c r i p t i o n a t t h e e n d of
t h i s s e c t i o n o n h o w t o r e c o g n i z e w h e n o n e of t h e m i s
o c c u r r i n g , p r o v i d e s m o t i v a t i o n f o r t h e u s e of t h e
a l g o r i t h m o u t l i n e d i n S e c t i o n 3 a s a m e a n s f o r
r e p a i r i n g c o m m u n i c a t i o n p r o b l e m s We w i l l o n l y d i s c u s s
r e f e r e n t c o n f u s i o n tn t h i s p a p e r The o t h e r f o r m s of
c o n f u s i o n - A c t i o n Goal, a n d C o g m t i v e L o a d - a r e
d e s c r i b e d i n [11 13] A n o t h e r c a t e g o r i z a t i o n of
c o n f u s m n s t h a t l e a d t o c o n v e r s a t i o n f a i l u r e c a n b e
f o u n d in [22]
• F i g u r e 2: A t a x o n o m y of c o n f u s m n s
R e f e r e n t ~ o n f u s l o n o c c u r s w h e n t h e l i s t e n e r is
u n a b l e to c o r r e c t l y d e t e r m i n e w h a t t h e s p e a k e r i s
r e f e r r i n g t o w i t h a p a r t i c u l a r d e s c r l p t m n [t o c c u r s
w h e n t h e d e s c r i p t i o n s In t h e u t t e r a n c e a r e a m b i g u o u s
o r i m p r e c i s e , w h e n t h e r e IS c o n f u s i o n b e t w e e n t h e
s p e a k e r a n d l i s t e n e r a b o u t w h a t t h e c u r r e n t f o c u s o r
c o n t e x t Is, o r w h e n t h e d e s c r i p t i o n s in t h e u t t e r a n c e
a r e e i t h e r i n c o r r e c t o r i n c o m p a t i b l e w i t h t h e c u r r e n t
o r g l o b a l c o n t e x t
E r r o n e o u s S p e c i f i c i t y
A m b i g u o u s ( a n d t h u s , i m p r e c i s e ) d e s c n p t x o n s c a n
c a u s e c o n f u s i o n a b o u t t h e r e f e r e n t E x c e r p t 2 b e l o w
i l l u s t r a t e s a c a s e w h e r e t h e s p e a k e r ' s d e s c r i p t i o n is
u n d e r s p e c x f l e d - i t d o e s n o t p r o v i d e e n o u g h d a t e d t o
p r u n e t h e s e t of p o s s i b l e r e f e r e n t s d o w n t o o n e
E x c e r p t 2 ( P a c e - t o - F a c e )
S 1 And n o w t a k e t h e l i t t l e r e d
3 p e g ,
[P t a k e s PLUG]
3 Yes,
4 a n d p l a c e i t xn t h e h o l e a t t h e
5 g r e e n e n d
[P s t a r t s t o p u t PLUG i n t o OUTLETR of MAINTUBE]
6 no
7 t h e - - i n t h e g r e e n t h i n g
[P p u t s PLUG i n t o g r e e n p a r t of PLUNGER]
P: 8 Okay
In L i n e 4 a n d 5, S d e s c r i b e s t h e l o c a t i o n t o p l a c e a p e g
i n t o a h o l e b y g i v i n g s p a t i a l i n f o r m a t i o n S i n c e t h e
l o c a t i o n i s g i v e n r e l a t i v e t o a n o t h e r l o c a t i o n b y " i n t h e
h o l e a t t h e g r e e n e n d " , i t d e f i n e s a r e g i o n w h e r e t h e
p e g m i g h t go i n s t e a d of a s p e c i f i c l o c a t i o n In t h i s
p a r t i c u l a r c a s e , t h e r e a r e t h r e e p o s s i b l e h o l e s to
c h o o s e f r o m t h a t a r e n e a r t h e g r e e n e n d T h e l i s t e n e r
c h o o s e s o n e - t h e w r o n g o n e - a n d i n s e r t s t h e p e g
i n t o i t B e c a u s e t h i s d i a l o g u e t o o k p l a c e f a c e t o f a c e ,
S i s a b l e t o c o r r e c t t h e a m b i g u i t y i n L i n e s 6 a n d 7
A s p e a k e r ' s d e s c r i p t i o n c a n b e i m p r e c i s e i n
s e v e r a l p o s s i b l e w a y s (1) It m a y c o n t a i n f e a t u r e s t h a t
d o n o t r e a d i l y a p p l y i n t h e d o m a i n In f i n e 3, E x c e r p t
3, t h e f e a t u r e " f u n n y " h a s n o r e l e v a n c e t o t h e l i s t e n e r
It i s n o t u n t i l A p r o v i d e s a f u l l e r d e s c r i p t i o n i n L i n e s 5
t o 8 t h a t E i s a b l e t o s e l e c t t h e p r o p e r p i e c e (2) It
m a y u s e a v a g u e h e a d n o u n c o u p l e d w i t h f e w o r no
f e a t u r e v a l u e s ( a n d c o n t e x t a l o n e d o e s n o t n e c e s s a r i l y
s u f f i c e t o d i s t i n g u i s h t h e o b j e c t ) In E x c e r p t 4, Line 9,
" a t t a c h m e n t " i s v a g u e b e c a u s e a l l o b j e c t s in t h e
d o m a i n a r e a t t a c h a b l e p a r t s T h e e x p e r t ' s u s e of
" a t t a c h m e n t " w a s m o s t l i k e l y t o s i g n a l t h e a c t i o n t h e
a p p r e n t i c e c a n e x p e c t t o t a k e n e x t The u s e of t h e
f e a t u r e v a l u e " c l e a r ' * p r o v i d e s l i t t l e b e n e f i t e i t h e r
b e c a u s e t h r e e c l e a r , u n u s e d p a r t s e x i s t The s i z e
d e s c r i p t o r " l i t t l e " p r u n e s t h i s s e t of p o s s i b l e r e f e r e n t s
d o w n t o t w o c o n t e n d e r s (3) E n o u g h f e a t u r e v a l u e s a r e
p r o v i d e d b u t a t l e a s t o n e v a l u e is t o o v a g u e l e a d i n g t o
t r o u b l e In E x c e r p t 5, Line 3, t h e u s e of t h e a t t r i b u t e
v a l u e " r o u n d e d " t o d e s c r i b e t h e s h a p e d o e s n o t
s u f f i c i e n t l y r e d u c e t h e s e t of f o u r p o s s i b l e r e f e r e n t s ( t h o u g h , i n t h i s p a r t i c u l a r i n s t a n c e , A c o r r e c t l y
i d e n t i f i e s i t ) b e c a u s e t h e t e r m is a p p l i c a b l e t o
n u m e r o u s p a r t s In t h e d o m m n A m o r e p r e c i s e s h a p e
d e s c r i p t o r s u c h a s " b e l l - s h a p e d " o r " c y l i n d r i c a l " w o u l d
h a v e b e e n m o r e b e n e f i c i a l t o t h e l i s t e n e r ,
E x c e r p t 3 ( T e l e p h o n e )
E: I All r i g h t
2 Now
3 T h e r e ' s a n o t h e r f u n n y l i t t l e
4 r e d t h i n g , a [A i s c o n f u s e d , e x a m i n e s b o t h NOZZLE
SX.,mr-VALVE ]
5 l i t t l e t e e n y r e d t h i n g t h a t ' s
6 s o m e - - s h o u l d b e s o m e w h e r e on
7 t h e d e s k , t h a t h a s u m - - t h e r e ' s
8 l i k e t e e t h on o n e e n d [E t a k e s SLIDEVALVE]
a n d
A: 9 Okay
E: 10 I t ' s a f u n n y - l o o - - h o l l o w ,
11 h o l l o w p r o j e c t i o n on o n e e n d
12 a n d t h e n t e e t h on t h e o t h e r
E x c e r p t 4 ( T e l e t y p e )
A: I t a k e t h e r e d t h i n g w i t h t h e
2 p r o n g s o n i t
3 a n d f i t i t o n t o t h e o t h e r h o l e
4 of t h e c y l i n d e r
5 s o t h a t t h e p r o n g s a r e
6 s t i c k i n g o u t
2O7
Trang 5A: 8 n o w t a k e t h e c l e a r l i t t l e
9 a t t a c h m e n t
10 a n d p u t o n t h e h o l e w h e r e y o u
11 j u s t p u t t h e r e d c a p o n
12 m a k e s u r e it p o i n t s
13 u p w a r d
R: 14 o k
F, x e e r p t 5 ( T e l e t y p e )
S; I Ok,
2 p u t t h e r e d n o z z l e o n t h e o u t l e t
3 of t h e r o u n d e d c l e a r c h a m b e r
4 o k ?
A: 5 got it
I m p r o p e r F o c u s
F o c u s c o n f u s i o n c a n o c c u r w h e n t h e s p e a k e r s e t s
u p o n e f o c u s a n d t h e n p r o c e e d s w i t h a n o t h e r o n e
w i t h o u t l e t t i n g t h e l i s t e n e r k n o w of t h e s w i t c h (i.e., a
f o c u s s h i f t o c c u r s w i t h o u t a n y i n d i c a t i o n ) An o p p o s i t e
p h e n o m e n o n c a n a l s o h a p p e n - t h e l i s t e n e r may feel
t h a t a f o c u s s h i f t h a s t a k e n p l a c e w h e n t h e s p e a k e r
a c t u a l l y n e v e r i n t e n d e d o n e T h e s e r e a l l y a r e v e r y
s i m i l a r - o n e Is viewed m o r e s t r o n g l y f r o m t h e
p e r s p e c t i v e of t h e s p e a k e r a n d t h e o t h e r f r o m t h e
l i s t e n e r
E x c e r p t 6 b e l o w l U u s t r a t e s a n m s t a n c e of t h e
f i r s t t y p e of f o c u s c o n f u s i o n In t h e e x c e r p t , t h e
s p e a k e r (S) s h i f t s f o c u s w i t h o u t n o t i f y i n g t h e l i s t e n e r
(P) of t h e s w i t c h As t h e e x c e r p t b e g i n s , P ,s h o l d i n g
t h e TUBEBASE S p r o v i d e s in Lines 1 to 16
m s t r u c t z o n s f o r P to a t t a c h t h e CAP a n d t h e SPOUT to
o u t l e t s OUTLETI a n d OUTLET2, r e s p e c t i v e l y , o n t h e
MAINTUSE U p o n P ' s s u c c e s s f u l c o m p l e t i o n of t h e s e
a t t a c h m e n t s S s w i t c h e s f o c u s m Lines 17 to 20 to t h e
TUSESASE a s s e m b l y a n d r e q u e s t s P to s c r e w tt on to
t h e b o t t o m of t h e M,e/NTUSE White P c o m p l e t e s t h e
t a s k S r e a l i z e s s h e left o u t a s t e p in t h e a s s e m b l y -
t h e p l a c e m e n t of t h e SLIDEVALVE i n t o OUTLET2 of t h e
M,eJNTUSE b e f o r e t h e SPOUT ts p l a c e d o v e r t h e s a m e
o u t l e t S a t t e m p t s to c o r r e c t h e r m i s t a k e by
r e q u e s t i n g P to r e m o v e " t h e p i e s "~ p i e c e in ~ n e s 22
a n d 23 S i n c e S n e v e r i n d i c a t e d a s h i f t in f o c u s f r o m
t h e TUSESASE b a c k to t h e IPOUT, P m t e r p r e t s " t h e
p i e s " to r e f e r to t h e TUSESASE
E x c e r p t 6 ( F a c e - t o - F a c e )
S 1 And p l a c e
2 t h e b l u e c a p t h a t ' s l e f t
[P t a k e s CAP]
3 o n t h e s i d e h o l e s t h a t a r e
3The whole ward here i s " p l e e t i c " People in general
tend to be good ot p r o c e e d i n q b e f o r e h e o r i n 9 the whole
u t t e r o n c e or even the whole word
4 o n t h e c y l i n d e r , [P l a y s d o w n TUBEBASE]
5 t h e s i d e h o l e t h a t is f a r t h e s t
6 f r o m t h e g r e e n e n d [P p u t s CAP o n OUTLET! of MAINTUBE]
P: 7 Okay
S; 8 And t a k e t h e n o z z l e - l o o k i n g
9 p i e c e , [P g r a b s NOZZLE]
10 n o
11 I m e a n t h e c l e a r p l a s t i c o n e , [P t a k e s SPOUT]
12 a n d p l a c e it o n t h e o t h e r h o l e [P i d e n t i f i e s O ~ of MA1NTUBE]
13 t h a t ' s left,
14 s o t h a t n o z z l e p o i n t s a w a y
15 f r o m t h e [P i n s t a l l s SPOUT o n OUTLET2 of MAINTUBE]
16 r i g h t P: 17 Okay
S: 18 Now
19 t a k e t h e
20 c a p b a s e t h i n g [P t a k e s TUBEBASE]
21 a n d s c r e w it o n t o t h e b o t t o m , [P s o r e w s T U B E B A S E on)L~3NTUBE]
22, ooops, [S r e a l i z e s s h e h a s f o r g o t t e n t o h a v e P p u t
S L I D L ~ A L V E i n t o OUTLET2 of MAINTUBE]
23 u n - u n d o t h e p i e s [P s t a r t s t o t a k e TUBEBASE off MAINTUBE]
24 n o
25 t h e c l e a r p l a s t i c t h i n g t h a t I
26 t o l d y o u t o p u t o n [P r e m o v e s SPOUT]
27 sorry
28 And p l a c e t h e l i t t l e r e d t h i n g [P t a k e s $LID~ALVZ]
29 tn t h e r e f i r s t , [P m s e r t s S L X D ~ A L V Z i n t o OUTLET~ of M[AINT~E]
30 it f i t s l o o s e l y in t h e r e
E x c e r p t 7 b e l o w d e m o n s t r a t e s t h e l a t t e r t y p e of
f o c u s c o n f u s z o n t h a t o c c u r s w h e n t h e s p e a k e r (S) s e t s
u p o n e f o c u s - t h e M,4]NTUBE, w h i c h is t h e c o r r e c t
f o c u s In t h i s c a s e - b u t t h e n p r o c e e d s in s u c h a
m a n n e r t h a t t h e l i s t e n e r (J) t h i n k s a f o c u s s h i f t to
a n o t h e r p i e c e , t h e TUBESASE, h a s o c c u r r e d T h u s , Line 15 r e f e r s t o " t h e l o w e r s i d e h o l e in t h e
M,41NTUBE" f o r S a n d " t h e h o l e in t h e TUBEBASE" f o r
J J h a s no way of r e a l i z i n g t h a t h e h a s f o c u s e d
i n c o r r e c t l y u n l e s s t h e d e s c r i p t i o n a s h e i n t e r p r e t s it
d o e s n ' t h a v e a r e a l w o r l d c o r r e l a t e ( h e r e s o m e t h i n g
d o e s s a t i s f y t h e d e s c r i p t i o n s o J d o e s n ' t s e n s e a n y
p r o b l e m ) o r if, l a t e r in t h e e x c h a n g e , a c o n f l i c t a r i s e s
2O8
Trang 6p e r f o r m e d ) In Line 31, J i n s e r t s a p i e c e i n t o t h e
w r o n g h o l e b e c a u s e of t h e m i s u n d e r s t a n d i n g in Line 15
Line 31 h i n t s t h a t J may h a v e b e c o m e s u s p i c i o u s t h a t
a n a m b i g u i t y e x i s t e d b u t s i n c e t h e t a s k w a s
s u c c e s s f u l l y c o m p l e t e d (i.e., t h e r e d p i e c e fit i n t o t h e
h o l e in t h e b a s e ) , a n d s i n c e S did n o t p r o v i d e a n y
c l a r i f i c a t i o n , h e a s s u m e d h e w a s c o r r e c t
h c e r p t 7 ( T e l e p h o n e )
S: 1 U m now
2 Now w e ' r e g e t t i n g a l i t t l e
3 m o r e difficult
J: 4 ( l a u g h s )
S: 5 Pick o u t t h e l a r g e a i r t u b e
[ l p i c k s u p S A N D ]
6 t h a t h a s t h e p l u n g e r in it
[J p u t s d o w n STAND t a k e s PLUNGER/MAINTUB~
a s s e m b l y ]
J: 7 Okay
S: 8 And s e t it o n ~ts b a s e ,
[J p u t s d o w n idAINTUBE, s t a n d i n g v e r t i c a l l y , o n t h e
TABLE]
9 w h i c h is b l u e now,
10 r z g h t ?
[J h a s s h i f t e d f o c u s t o t h e TUBEBASE]
J: 11 Yeah
$, 12 Base is blue
13 Okay
14 Now
15 Y o u ' v e g o t a b o t t o m h o l e still
16 to be filled,
17 c o r r e c t ?
J: 18 Yeah
[J a n s w e r s t h i s w i t h MAINTUBE s t i l l s i t t i n t o n t h e
TABLE; h e s h o w s n o i n d i c a t i o n of w h a t
h o l e h e t h i n k s i8 m e a n t - t h e o n e o n
t h e MAINTUBE OUTLET2, o r t h e o n e in
t h e TUBEBASE]
[J
S
p i c k s
19 Okay
20 You h a v e o n e r e d p i e c e
21 r e m a m m 8 ?
u p ldA/NTUBE a s s e m b l y a n d l o o k s a t
TUBEBASE, r o t a t i n e t h e MAINTUBE s o
t h a t TUBP-BASE is p o i n t e d u p , a n d
s e e s t h e h o l e in i t ; h e t h e n l o o k s a t
t h e SLIDEVALVE]
J: 22 Yeah
3 23 Okay
24 Take t h a t r e d piece
[j t a k e s SIJDEVALVE]
25 I t ' s g o t f o u r l i t t l e f e e t o n
26 it?
J: 27 Yeah
S; 28 And p u t t h e small e n d i n t o
29 t h a t h o l e on t h e a i r t u b e - -
30 o n t h e big t u b e
[J s t a r t s J; 31 On t h e v e r y b o t t o m ? t o p u t it i n t o t h e b o t t o m h o l e of
TUBEBASE - t h o u g h h e i n d i c a t e s h e is
u n s u r e of h i m s e l f ] S: 32 On t h e b o t t o m ,
33 Yes
M i s f o c u s c a n a l s o o c c u r w h e n t h e s p e a k e r
i n a d v e r t e n t l y l e f t s t o d i s t i n g u i s h t h e p r o p e r f o c u s
b e c a u s e h e did n o t n o t i c e a p o s s i b l e a m b i g u i t y ; o r
w h e n , t h r o u g h n o f a u l t of t h e s p e a k e r , t h e l i s t e n e r j u s t
fails t o r e c o g n i z e a s w i t c h in f o c u s i n d i c a t e d by t h e
s p e a k e r ~ x c e r p t 7 a b o v e is a n e x a m p l e of t h e f i r s t
t y p e b e c a u s e S f a i l e d t o n o t i c e t h a t a n a m b l g u z t y
e x i s t e d s i n c e h e n e v e r e x p l i c i t l y b r o u g h t t h e TUBEBASE
e i t h e r i n t o o r o u t of f o c u s He j u s t a s s u m e d t h a t J
h a d t h e s a m e p e r s p e c t i v e a s hzm - a p e r s p e c t i v e in
w h i c h u o a m b i g u i t y o c c u r r e d
Wrong Context
C o n t e x t d i f f e r s f r o m f o c u s The c o n t e x t of a
p o r t i o n of a c o n v e r s a t i o n is c o n c e r n e d with t h e p o : n t
of t h e d i s c u s s i o n in t h a t f r a g m e n t a n d with t h e s e t of
o b j e c t s r e l e v a n t t o t h a t d i s c u s s i o n , t h o u g h n o t
a t t e n d e d t o c u r r e n t l y F o c u s p e r t a i n s to t h e e l e m e n t s
w h i c h a r e c u r r e n t l y b e i n g a t t e n d e d to in t h e c o n t e x t
F o r e x a m p l e , two p e o p l e c a n s h a r e t h e s a m e c o n t e x t
b u t h a v e d i f f e r e n t f o c u s a s s i g n m e n t s wt~hm it - w e ' r e
b o t h t a l k i n g a b o u t t h e w a t e r p u m p b u t y o u ' r e
d e s c r i b i n g t h e MA/NTUB£ a n d I'm d e s c r l b m g t h e
AIRCH,4MB£,q A l t e r n a t i v e l y , we c o u l d JUst be u s l n g
d i f f e r e n t c o n t e x t s - I t h i n k y o u ' r e t a l k i n g a b o u t t a k i n g
t h e p u m p a p a r t b u t y o u ' r e t a l k i n g a b o u t r e p l h ^ l n g t h e
p u m p w i t h n e w p a r t s - m b o t h c a s e s we m~v be
s h a r i n g t h e s a m e f o c u s - t h e p u m p - b u t o u r c o n t e ~ , s
a r e t o t a l l y off f r o m o n e a n o t h e r ~ The k i n d s of
m i s u n d e r s t a n d i n g s t h a t c a n o c c u r b e c a u s e of c o n t e x t
p r o b l e m s a r e s i m i l a r to t h o s e f o r f o c u s p r o b l e m s : (1)
t h e s p e a k e r might s e t u p o r be xn o n e c o n t e x t for a
d i s c u s s i o n a n d t h e n p r o c e e d in a n o t h e r o n e w i t h o u t
e f f e c t i v e l y l e t t i n g t h e l i s t e n e r k n o w of t h e c h a n g e , (2)
t h e l i s t e n e r may feel a c h a n g e in c o n t e x t h a s t a k e n
p l a c e w h e n in f a c t t h e s p e a k e r n e v e r I n t e n d e d one, o r (:3) t h e L i s t e n e r fails t o r e c o g n i z e a n i n d i c a t e d c o n t e x t
s w i t c h by t h e s p e a k e r C o n t e x t a f f e c t s r e f e r e n c e
b e c a u s e it h e l p s d e f i n e t h e s e t of a v a i l a b l e o b l e c t s t h a t
a r e p o s s i b l e c o n t e n d e r s f o r t h e r e f e r e n t of t h e
s p e a k e r ' s d e s c r i p t i o n s If t h e c o n t e x t s of t h e s p e a k e r
a n d l i s t e n e r differ, t h e n m | s r e f e r e n c e might r e s u l t
B a d AnaloEy
a n a l o g i e s ) is a u s e f u l way to h e l p d e s c r l b e an o b j e c t by
a t t e m p t l n g to be m o r e p r e c i s e by u s i n g s h a r e d p a s t
e x p e m e n c e a n d k n o w l e d g e - e s p e c : a l l y s h a p e a n d
f u n c t i o n a l r e f o r m a t i o n If t h a t p a s t e x p e r x e n c e o r
k n o w l e d g e d o e s n ' t c o n t a i n t h e r e f o r m a t i o n t h e s p e a k e r
a s s u m e s it d o e s o r i s n ' t t h e r e , t h e n t r o u b l e o c c u r s
T h u s o n e m o r e way r e f e r e n t c o n f u s i o n can o c c u r Is by
d e s c r i b i n g a n oh}act u s i n g • p o o r a n a l o g y An a n a l o g y
u s e d t o d e s c r i b e a n o b j e c t m i g h t n o t be s p e c : f i c
4Groez [14, lS] would dem~ril~ t h i s as o d i f f e r e n c e in
" t a s k DIane J ~ i l e Rai¢ltlNnt [2e, 21] m~uld say that the
"c0mlmmjcativa gCNlie" dJffare¢l
2O9
Trang 7e n o u g h - c o n f u s i n g t h e l i s t e n e r b e c a u s e s e v e r a l p i e c e s
m i g h t c o n f o r m t o t h e a n a l o g y o r , tn f a c t , n o n e a t a l l
a p p e a r t o f i t b e c a u s e d i s c o v e r i n g a m a p p i n g b e t w e e n
t h e a n a l o g o u s o b j e c t a n d s o m e p i e c e i n t h e
e n v i r o n m e n t Is t o o d i f f i c u l t In E x c e r p t 8, J a t f i r s t
h a s t r o u b l e c o r r e c t l y s a t i s f y i n g A's f u n c t i o n a l a n a l o g y
" s t o p p e r " i n " t h e bag b l u e s t o p p e r " , b u t f i n a l l y s e l e c t s
w h a t h e c o n s i d e r s t o b e t h e c l o s e s t m a t c h t o
" s t o p p e r "
E x c e r p t 8 ( T e l e p h o n e )
A: I Okay Now
2 take the big blue
3 stopper that's laying a r o u n d
[J g r a b s ~diCI4AMBER]
4 a n d take the black
5, r i n g - -
J: 6 The b i g b l u e s t o p p e r ?
[J i s c o n f u s e d a n d t r i e s t o c o m m u n i c a t e i t t o A; h e
is h o l d i n g t h e AIRCHAMBER h e r e ]
A 7 Yeah
8 the blg blue s t o p p e r
9 a n d t h e b l a c k r i n g
[J d r o p s AIRCHAMBER a n d t a k e s t h e O - R I N G a n d
t h e TUBEBASE]
In o t h e r c a s e s tt m i g h t be t o o s p e c i f i c -
c o n f u s i n g t h e l i s t e n e r b e c a u s e n o n e of t h e a v a i l a b l e
r e f e r e n t s a p p e a r to f i t it In Line 8 of E x c e r p t 6,
" n o z z l e - l o o k i n g " f o r m s a p o o r s h a p e a n a l o g y b e c a u s e
t h e o b j e c t b e i n g r e f e r r e d t o a c t u a l l y Is a n e l b o w -
s h a p e d s p o u t The " n o z z l e - l o o k l n g " p a r t of t h e
d e s c r i p t i o n c o n v i n c e d t h e l i s t e n e r t h a t w h a t h e w a s
l o o k i n g f o r w a s s o m e t h i n g s p e c i f i c l i k e a n o z z l e ( w h i c h
xs a s m a l l s p o u t ) S o m e t i m e s , w h e n a n o b l e c t xs a c l e a r
r e p r e s e n t a t i v e of a s p e c i f i e d a n a l o g y c l a s s , t h e
a p p r e n t 2 c e m a y b e c o m e c o n f u s e d , w o n d e r i n g w h y t h e
e x p e r t b o t h e r e d to f o r m a n a n a l o g y m s t e a d of j u s t
d i r e c t l y d e s c r i b i n g t h e o b j e c t a s a m e m b e r of t h e c l a s s
H e n c e , tt w o u l d n o t be s u r p r i s i n g d t h e a p p r e n t i c e
t g n o r e u t h e b e s t r e p r e s e n t a t n v e of t h e c l a s s f o r s o m e
l e s s o b v i o u s e x e m p l a r T h u s , f o r e x a m p l e , It ts b e t t e r t o
s a y " n o z z l e " i n s t e a d of " n o z z l e - l o o k i n g " In E x c e r p t 9,
t h e d e s c r i p t i o n " h i p p o p o t a m u s f a c e s h a p e " ( a s h a p e
analogy) tn Lines 2 a n d 3, and " c h a m p a g n e top" (a
s h a p e a n a l o g y ) in Line 9 e r e t o o s p e c l h c a n d t h e
h s t e n e r ts u n a b l e t o e a s i l y f i n d s o m e t h i n g c l o s e e n o u g h
to m a t c h e i t h e r of t h e m He c a n ' t d i s c o v e r a m a p p i n g
b e t w e e n t h e o b l e c t in t h e a n a l o g y a n d o n e in t h e r e a l
w o r l d
E x c e r p t 9 ( A u d i o t a p e )
M; I t a k e t h e b r i g h t p l n k f l a t
2 p i e c e of h i p p o p o t a m u s f a c e
3 s h a p e p i e c e of p l a s t i c
4 a n d y o u n o t i c e t h a t t h e t w o
5 h o l e s o n xt
[M i s t r ~ t n g t o r e f e r t o BASEVALVE]
6 m a t c h
7 a l o n g w i t h t h e two
8 p e g h o l e s o n t h e
9 c h a m p a g n e t o p s o r t of
10 l o o k i n g b o t t o m t h a t h a d
[M i s t r y i n E t o r e f e r t o TUBEBASE]
D e s c r i p t i o n i n c o m p a t i b i l i t y
I n c o m p a t i b l e d e s c r i p t i o n s c a n l e a d t o c o n f u s i o n
a l s o A d e s c r i p t i o n i s i n c o m p a t i b l e w h e n (1) o n e o r
m o r e of t h e s p e c i f i e d c o n d i t i o n s , i.e., t h e f e a t u r e
v a l u e s , do n o t s a t i s f y a n y of t h e p i e c e s ; (2) w h e n o n e
o r m o r e s p e c i f i e d c o n s t r a i n t s do n o t h o l d (e.g s a y i n g
" t h e l o o s e o n e " w h e n a l l o b j e c t s a r e t i g h t l y a t t a c h e d )
o r (3) if n o o n e o b j e c t s a t i s f i e s al_~l of t h e f e a t u r e s
s p e c i f i e d i n t h e d e s c r i p t i o n In L i n e s 7 a n d 8 of
E x c e r p t 9 a b o v e , M's u s e of " t h e t w o p e g h o l e s " l e a d s
t o b e w i l d e r m e n t f o r t h e l i s t e n e r b e c a u s e t h e d e s c r i b e d
o b j e c t h a s n o h o l e s i n it M a c t u a l l y m e a n t " t w o p e g s "
2.2.2 D e t e c t i n g m i s c o m m u n i c a t l o n
P a r t of o u r r e s e a r c h h a s b e e n t o e x a m i n e h o w a
l i s t e n e r d i s c o v e r s t h e n e e d f o r a r e p a i r of a n
u t t e r a n c e o r a d e s c r i p t i o n d u r i n g c o m m u n i c a t i o n The
i n c o m p a t i b i l i t y of a r e f e r e n t o r a c t i o n is o n e s i g n a l of
p o s s i b l e t r o u b l e The a p p e a r a n c e of a n o b s t a c l e t h a t
b l o c k s o n e f r o m a c h i e v i n g a g o a l is a n o t h e r i n d i c a t i o n
of a p r o b l e m
I n c o m p a t i b i l l t y
Two k i n d s of i n c o m p a t ~ b t l t t y , a c t i o n o r r e f e r e n t
a p p e a r In t h e t a x o n o m y of c o n f u s i o n s T h e s t r o n g e s t
h i n t t h a t t h e r e is a r e f e r e n c e p r o b l e m o c c u r s w h e n t h e
l i s t e n e r f i n d s n o r e a l w o r l d o b j e c t to c o r r e s p o n d to t h e
s p e a k e r ' s d e s c r i p t i o n T h i s c a n o c c u r w h e n (1) o n e o r
m o r e of t h e s p e c i f i e d f e a t u r e v a l u e s xn t h e d e s c r i p t i o n
a r e n o t s a t i s f i e d by a n y of t h e p i e c e s ( e g s a y i n g " t h e
o r a n g e c a p " w h e n n o n e of t h e o b j e c t s a r e o r a n g e ~ {2)
w h e n o n e o r m o r e s p e c i f i e d c o n s t r a i n t s do n o t h o l d (e.g., s a y i n g " t h e r e d p l u g t h a t f i t s l o o s e l y " w h e n a l l
t h e r e d p l u g s a t t a c h t i g h t l y ) , o r (3) If no o n e o b j e c t
s a t i s f i e s a l l of t h e f e a t u r e s s p e c i f i e d m t h e d e s c r i p t i o n (I.e., t h e r ' e - t s , f o r e a c h f e a t u r e , a n o b j e c t t h a t e x h i b i t s
t h e s p e c i f i e d f e a t u r e v a l u e , b u t n o o n e o b j e c t e x h i b i t s
a l l of t h e v a l u e s ) An a c t i o n p r o b l e m xs l i k e l y ~f I l) t h e
l i s t e n e r c a n n o t p e r f o r m t h e a c t i o n s p e c i f i e d by t h e
s p e a k e r b e c a u s e of s o m e o b s t a c l e ; (2) t h e h s t e n e r
p e r f o r m s t h e a c t i o n b u t d o e s n o t a r r l v e a t i t s i n t e n d e d
e f f e c t (I.e., a s p e c i f i e d o r d e f a u l t c o n s t r a m t l s n t
s a t i s f i e d ) ; o r (3) t h e c u r r e n t a c t i o n a f f e c t s a p r e v i o u s
a c t i o n tn a n a d v e r s e way, y e t t h e s p e a k e r h a s g i v e n no
s i g n of a n y i m p o r t a n c e t o t h i s s i d e - e f f e c t
G o a l o b s t a c l e
A g o a l o b s t a c l e o c c u r s w h e n a g o a l ( o r s u b g o a [ )
o n e is t r y i n g to a c h i e v e ts b l o c k e d T h i s b l o c k a g e c a n
r e s u l t m c o n f u s i o n f o r t h e h s t e n e r b e c a u s e he d i d n o t
e x p e c t t h e s p e a k e r t o g i v e him t a s k s t h a t c o u l d n o t b e
a c h i e v e d O f t e n t h o u g h , i t p o i n t s o u t f o r t h e h s t e n e r
t h a t s o m e m l s c o m m u n i c a t i o n ( s u c h a s m l s r e f e r e n c e ) h a s
o c c u r r e d
G o a l r e d u n d a n c y
G o a l r e d u n d a n c y o c c u r s w h e n t h e r e q u e s t e d g o a l ( o r s u b g o a l ) is a l r e a d y s a t i s f i e d In s o m e s e n s e , xt xs a
s p e c i a l k l n d of g o a l o b s t a c l e w h e r e t h e g o a l t o be
f u l f i l l e d i s b l o c k e d b e c a u s e i t i s a l r e a d y s a t i s f i e d It is
a s i m p l e g o a l o b s t a c l e b e c a u s e n o t h m g h a s t o b e d o n e
t o g e t a r o u n d it H o w e v e r , i t c a n l e a d t o c o n f u s i o n on
210
Trang 8t h e p a r t l i s t e n e r s b e c a u s e t h e y m a y s u s p e c t t h e y
m i s u n d e r s t o o d w h a t t h e s p e a k e r h a s r e q u e s t e d s i n c e
t h e y w o u l d n ' t e x p e c t a r e a s o n a b l e s p e a k e r Lo r e q u e s t
t h e p e r f o r m a n c e of a n a l r e a d y c o m p l e t e d a c t i o n I t
p r o v i d e s a h i n t t h a t m i s c o m m u m c a t i o n h a s o c c u r r e d
3 R e p a i r i n g R e f e r e n c e F a i l u r e s
3 I I n t r o d u c t i o n
T h e previous section dlustrated h o w t a s k -
oriented natural l a n g u a g e m t e r a c t l o n s in the real
world c a n i n d u c e contextually p o o r utterances Given
all the possibilities for confusion, w h e n confusions d o
occur, they m u s t b e resolved If the task is to b e
p e r f o r m e d T h i s s e c t i o n e x p l o r e s t h e p r o b l e m o f f i x i n g
r e f e r e n c e f a i l u r e s
R e f e r e n c e I d e n t i f i c a t i o n i s a s e a r c h p r o c e s s w h e r e
a l i s t e n e r l o o k s f o r s o m e t h i n g i n t h e w o r l d t h a t
c o m p u t a t l o n a l s c h e m e for performing reference h a s
evolved from w o r k b y other artificial intelligence
researchers (e.g., see [14]) That tradltlonal a p p r o a c h
s u c c e e d s if a referent ~s found, or falls d n o referent
ts f o u n d {see Figure 3 ( a ) ) H o w e v e r , a reference
identlficatlon c o m p o n e n t m u s t be m o r e versatile t h a n
those c o n s t r u c t e d m the traditional m a n n e r T h e
excerpts provided m the prevlous section s h o w that
t h e t r a d i t i o n a l a p p r o a c h i s w r o n g b e c a u s e people's r e a l
behavlor zs m u c h m o r e elaborate In particular
hsteners often find the correct referent e v e n w h e n the
speaker's descrlpt)on does not describe a n y object In
the world For example, a s p e a k e r could descrlbe a
blue block as the "turquoise block." M o s t listeners
w o u l d go a h e a d a n d a s s u m e that the blue block w a s the
o n e the s p e a k e r meant
A k e y feature to reference identlficatlon is
"negotlatlon." Negotlatlon in reference ldentlhcatlon
c o m e s in two forms First It c a n o c c u r b e t w e e n the
listener a n d the speaker T h e listener c a n step back,
e x p a n d greatly o n the speaker's descrlptlon of a
plausible referent, a n d a s k for c o n h r m a t l o n that h e
h a s indeed f o u n d the correct referent For example, a
h s t e n e r could mltlate negotiation wlth 'Tin confused
Are y o u talking a b o u t the thlng that is klnd of flared
at the top? C o u p l e inches long It's kind of blue."
Second negotiation c a n be wlth oneself Thls type of
negotiation, called self-negotlatlon Ls the o n e that w e
are most c o n c e r n e d wlth in thls research T h e listener
conslders aspects of the speaker's descrzptlon, the
context of the c o m m u m c a t l o n , a n d the listener's o w n
abdltles H e t h e n a p p h e s that d e h b e r a t l o n to d e t e r m i n e
w h e t h e r o n e referent candldate :s better t h a n a n o t h e r
or if n o candidate Is found, w h a t are the m o s t likely
places for error or confuslon S u c h negotlatlon c a n
result in the listener testing w h e t h e r or not a
descrlptlons c a n influence a listener's perception of
the world T h e listener m u s t ask himself w h e t h e r h e
c a n percelve o n e of the oblects in the world the w a y
the s p e a k e r described it in s o m e cases, the listener's
perceptlon m a y overrule the descrlptlon b e c a u s e the
listener can't percelve ~t the w a y the s p e a k e r
described it
To r e p a i r t h e t r a d i t i o n a l a p p r o a c h w e h a v e
developed a n a l g o r i t h m t h a t c a p t u r e s f o r c e r t a i n c a s e s
t h e l i s t e n e r ' s a b d i t y t o n e g o t i a t e w i t h h i m s e l f f o r a
r e f e r e n t It c a n l o o k f o r a r e f e r e n t a n d If I t d o e s n ' t
t h a t m i g h t w o r k , a n d t h e n l o o s e n t h e s p e a k e r ' s
d e s c r i p t i o n u s i n g k n o w l e d g e a b o u t t h e s p e a k e r , t h e
c o n v e r s a t i o n , a n d t h e l i s t e n e r h i m s e l f T h u s t h e
r e f e r e n c e p r o c e s s b e c o m e s m u l t i - s t e p a n d r e s u m a b l e
T h i s c o m p u t a t i o n a l m o d e l , w h i c h I c a l l "FWIM" f o r " F i n d
W h a t I M e a n " , i s m o r e f a i t h f u l t o t h e d a t a t h a n t h e
t r a d i t i o n a l m o d e l ( s e e F i g u r e 3 ( b ) )
C u r r e n t I_ ~ RefePence ~u =
Component
~ m i ~ = t
C u r r e n t Reference -~ ~,,=¢ = Component
~ ~J~milure
R e l a x a t i o n 1 Component T¢.-,,- u
F i g u r e 3: A p p r o a c h e s t o reference ] d e n t d l c a t l o n
O n e m e a n s of m a k i n g s e n s e of a n a p p r o x l m a t e
d e s c r i p t i o n i s t o d e l e t e o r r e p l a c e p o r t l o n s of i t t h a t
d o n ' t m a t c h o b j e c t s In t h e h e a t e r ' s w o r l d [n o u r
p r o g r a m we a r e u s l n g " r e l a x a t i o n " t e c h n i q u e s t o
c a p t u r e t h i s b e h a v i o r O u r r e f e r e n c e i d e n t l h c a t l o n
m o d u l e t r e a t s d e s c r i p t i o n s a s a p p r o x i m a t e It r e l a x e s
a d e s c r i p t i o n i n o r d e r t o f i n d a r e f e r e n t w h e n t h e
h t e r a l c o n t e n t of t h e d e s c r i p t i o n f a l l s t o p r o v i d e t h e
n e e d e d I n f o r m a t i o n R e l a x a t i o n h o w e v e r , i s n o t
p e r f o r m e d b l i n d l y o n t h e d e s c r i p t i o n We t r y t o m o d e l
a p e r s o n ' s b e h a v i o r b y d r a w l n g o n s o u r c e s of
k n o w l e d g e u s e d b y p e o p l e We h a v e d e v e l o p e d a
c o m p u t a t i o n a l m o d e l t h a t c a n r e l a x a s p e c t s o f a
d e s c r l p t l o n u s i n g m a n y of t h e s e s o u r c e s of k n o w l e d g e
R e l a x a t i o n t h e n b e c o m e s a f o r m of c o m m u m c a t l o n
r e p a i r [ 4 ] t h a t h e a r e r s c a n u s e
3 2 T h e r e l a x a t i o n c o m p o n e n t
W h e n a d e s c r i p t i o n f a i l s t o d e n o t e a r e f e r e n t In
t h e r e a l w o r l d p r o p e r l y , I t Is p o s s i b l e t o r e p a i r tt b y a
r e l a x a t l o n p r o c e s s t h a t i g n o r e s o r m o d i f i e s p a r t s of t h e
d e s c r l p t l o n S i n c e a d e s c r i p t i o n c a n s p e c l f y m a n y
f e a t u r e s of a n o b j e c t , t h e o r d e r In w h i c h p a r t s of It
a r e r e l a x e d Is c r u c i a l (i.e r e l a x i n g Ln d i f f e r e n t o r d e r s
c o u l d y i e l d m a t c h e s t o d i f f e r e n t o b j e c t s ) T h e r e a r e
s e v e r a l k i n d s of r e l a x a t i o n p o s s i b l e One c a n i g n o r e a
c o n s t i t u e n t , r e p l a c e It w i t h s o m e t h i n g c l o s e , r e p l a c e i t
w i t h a r e l a t e d v a l u e , o r c h a n g e f o c u s (i.e c o n s i d e r a
d i f f e r e n t g r o u p of o b j e c t s ) T h i s s e c t i o n d e s c r l b e s t h e
o v e r a l l r e l a x a t l o n c o m p o n e n t t h a t d r a w s o n k n o w l e d g e
s o u r c e s a b o u t d e s c r i p t i o n s a n d t h e r e a l w o r l d a s i t
t r i e s t o r e l a x a n e r r o r f u l d e s c r i p t i o n t o o n e f o r w h i c h
a r e f e r e n t c a n b e s d e n t l f i e d
3 2 1 F i n d a r e f e r e n t u s i n g a r e f e r e n c e m e c h a m s m
I d e n t i f y i n g t h e r e f e r e n t of a d e s c r i p t i o n r e q u i r e s
f i n d i n g a n e l e m e n t i n t h e w o r l d t h a t c o r r e s p o n d s t o t h e
s p e a k e r ' s d e s c r i p t i o n ( w h e r e e v e r y f e a t u r e s p e c i f i e d i n
t h e d e s c r i p t i o n i s p r e s e n t In t h e e l e m e n t i n t h e w o r l d
b u t n o t n e c e s s a r i l y v i c e v e r s a ) T h e i n i t i a l t a s k of o u r
Trang 9r e f e r e n c e m e c h a n i s m Is t o d e t e r m i n e w h e t h e r o r n o t a
s e a r c h of t h e ( t a x o n o m i c ) k n o w l e d g e b a s e t h a t we u s e
t o m o d e l t h e w o r l d Is n e c e s s a r y F o r e x a m p l e , t h e
r e f e r e n c e c o m p o n e n t s h o u l d n o t b o t h e r s e a r c h i n g -
u n l e s s s p e c i f i c a l l y r e q u e s t e d t o do so - f o r a r e f e r e n t
f o r i n d e f i n i t e n o u n p h r a s e s ( w h i c h u s u a l l y d e s c r i b e n e w
o r h y p o t h e t i c a l o b j e c t s ) o r e x t r e m e l y v a g u e
d e s c r i p t i o n s ( w h i c h do n o t c l e a r l y d e s c r i b e a n o b l e c t
b e c a u s e t h e y a r e c o m p o s e d of i m p r e c i s e f e a t u r e
values) A n u m b e r of aspects of discourse pragmattcs
c a n be u s e d in that determination (eg., the use of a
delctlc In a definite n o u n phrase, s u c h as "thls X" or
"the last X", hints that the object w a s either m e n t i o n e d
p r e v i o u s l y o r t h a t i t p r o b a b l y w a s e v o k e d by s o m e
p r e v i o u s r e f e r e n c e , a n d t h a t i t is s e a r c h a b l e ) b u t we
will n o t e x a m i n e t h e m h e r e
T h e k n o w l e d g e base contains linguistic
descriptions a n d a descrlptton of the listener's vlsual
s c e n e itself In o u r Implementation a n d algorithms, we
a s s u m e It is r e p r e s e n t e d In K L - O n e [3], a s y s t e m for
describing t a x o n o m i c knowledge K L - O n e is c o m p o s e d
of C O N C E P T s , R O L E s o n concepts, e n d links b e t w e e n
them A C O N C E P T Is like a set representing those
elements described b y it A S U P E R C link ( ' = = > " ) is
u s e d b e t w e e n c o n c e p t s to s h o w set Inclusion For
example, consider Figure 3 T h e S u p e r C from C o n c e p t B
to C o n c e p t A is like stating B C A for two sets A a n d
B A n INDIVIDUAL C O N C E P T ts u s e d to g u a r a n t e e that the
subset speclhed by a c o n c e p t Is u n i q u e T h e [ndlvldual
C o n c e p t D s h o w n m the figure Is d e h n e d to be a
u n i q u e m e m b e r of the subset specified by C o n c e p t
C R O L E s o n c o n c e p t s are like n o r m a l attributes a n d
slot hllers m o t h e r k n o w l e d g e representation
b e t w e e n the c o n c e p t a n d other c o n c e p t s
Concept
Concept
Figure 4: A K L - O n e T a x o n o m y
A s s u m i n g t h a t a s e a r c h of t h e k n o w l e d g e b a s e Is
c o n s i d e r e d n e c e s s a r y , t h e n a r e f e r e n c e s e a r c h
m e c h a n i s m ts r e v o k e d The s e a r c h m e c h a n i s m u s e s t h e
K L - O n e C l a s s t h e r [ 1 6 ] t o s e a r c h t h e k n o w l e d g e b a s e
t a x o n o m y T h l s s e a r c h Is c o n s t r a i n e d b y a f o c u s
m e c h a n l s m b a s e d on t h e o n e d e v e l o p e d by G r o s z [14]
The C l a s s a f l e r ' s p u r p o s e Is t o d i s c o v e r all a p p r o p r m t e
~ u b s u m p t l o n r e l a t i o n s h i p s b e t w e e n a n e w l y f o r m e d
d e s c r l p t t o n and all o t h e r descriptions In a g w e n
t a x o n o m y With respect to reference, t h i s m e a n s that
descrlptlon will be s u b s u m e d by tt after It has b e e n
classLhed rote the k n o w l e d g e base taxonomy If m o r e
than o n e candidate referent Is below ( w h e n a
descrlptlon A Is s u b s u m e d by B w e say A ts "below" B)
the classified description, then, unless a quantifier in
the description specified m o r e t h a n o n e element, the
speaker's description is ambiguous If exactly o n e
descr~ptlon Is below it, t h e n the intended referent is
a s s u m e d t o h a v e b e e n f o u n d F i n a l l y , if n o r e f e r e n t is
c o m p o n e n t i s i n v o k e d We will o n l y c o n s i d e r t h e l a s t
c a s e i n t h e r e s t of t h e p a p e r
3.2.2 C o l l e c t v o t e s f o r o r a g a i n s t r e l a x i n g t h e
d e s c r i p t i o n
It is n e c e s s a r y t o d e t e r m i n e w h e t h e r o r n o t t h e
l a c k of a r e f e r e n t f o r a d e s c r i p t i o n h a s t o do w i t h t h e
d e s c r i p t i o n i t s e l f (i.e r e f e r e n c e f a i l u r e ) o r o u t s i d e
f o r c e s t h a t a r e c a u s i n g r e f e r e n c e c o n f u s i o n F o r
e x a m p l e , t h e p r o b l e m m a y b e w i t h t h e flow of t h e
c o n v e r s a t i o n a n d t h e s p e a k e r ' s a n d h s t e n e r s
p e r s p e c t i v e s o n i t ; i t m a y b e d u e t o m c o r r e c t
a t t a c h m e n t of a m o d i f i e r ; i t m a y b e d u e t o t h e a c t i o n
r e q u e s t e d ; a n d so on P r a g m a t i c r u l e s a r e I n v o k e d to
d e c i d e w h e t h e r o r n o t t h e d e s c r x p t l o n s h o u l d be
r e l a x e d T h e s e r u l e s will n o t be d i s c u s s e d h e r e so we will a s s u m e t h a t t h e p r o b l e m l i e s in t h e s p e a k e r s
d e s c r i p t i o n
3.2.3 P e r f o r m t h e r e l a x a t i o n of t h e d e s c r i p t i o n
If r e l a x a t i o n Is d e m a n d e d , t h e n t h e s y s t e m m u s t (1) f i n d p o t e n t i a l r e f e r e n t c a n d i d a t e s , ( 2 l d e t e r m i n e
w h i c h f e a t u r e s in t h e s p e a k e r ' s d e s c r i p t i o n to r e l a x
a n d in w h a t o r d e r , a n d u s e t h o s e o r d e r e d f e a t u r e s to
o r d e r t h e p o t e n t i a l c a n d i d a t e s w i t h r e s p e c t to t h e
p r e f e r r e d o r d e r i n g of f e a t u r e s , a n d (3~ d e t e r m i n e t h e
p r o p e r r e l a x a t i o n t e c h n i q u e s to u s e a n d a p p l y t h e m to
t h e d e s c r i p t i o n
F i n d p o t e n t i a l r e f e r e n t c a n d i d a t e s
B e f o r e r e l a x a t i o n c a n t a k e p l a c e , p o t e n t i a l
c a n d i d a t e s f o r r e f e r e n t s ( w h i c h d e n o t e e l e m e n t s in t h e
l i s t e n e r ' s v i s u a l s c e n e ) m u s t f i r s t b e f o u n d T h e s e
c a n d i d a t e s a r e d i s c o v e r e d by p e r f o r m i n g a " w a l k " tn
t h e k n o w l e d g e b a s e t a x o n o m y in t h e g e n e r a l v l c l m t y of
t h e s p e a k e r s c l a s s i f i e d d e s c r i p t i o n A K L - O n e p a r t i a l
m a r c h e r is u s e d to d e t e r m m e h o w c l o s e t h e candidate
d e s c r i p t i o n s f o u n d d u r i n g t h e w a l k a r e to t h e s p e a k e r s
d e s c r i p t i o n , The p a r t i a l m e t c h e r g e n e r a t e s a n u m e r i c a l
s c o r e t o r e p r e s e n t how well the d e s c r l p t l o n s m a t c h ( a f t e r f i r s t g e n e r a t i n g s c o r e s a t t h e f e a t u r e l e v e l to
h e l p d e t e r m m e how t h e f e a t u r e s a r e t o be a l i g n e d e n d
h o w w e l l t h e y m a t c h ) T h i s s c o r e is b a s e d on
i n f o r m a t i o n a b o u t K L - O n e a n d d o e s n o t t a k e m t o
a c c o u n t a n y i n f o r m a t i o n a b o u t t h e t a s k d o m a i n The
o r d e r i n g of f e a t u r e s a n d c a n d i d a t e s f o r r e l a x a t i o n
d e s c r i b e d b e l o w t a k e s I n t o a c c o u n t t h e t a s k d o m a i n The s e t of b e s t d e s c r i p t i o n s r e t u r n e d by t h e m a r c h e r ( a s d e t e r m i n e d by s o m e c u t o f f s c o r e ) a r e s e l e c t e d a s
r e f e r e n t c a n d i d a t e s
O r d e r t h e f e a t u r e s a n d c a n d i d a t e s f o r r e l a x a t i o n
At t h i s p e a t t h e r e f e r e n c e s y s t e m i n s p e c t s t h e
s p e a k e r ' s d e s c r i p t i o n a n d t h e c a n d i d a t e s , d e c i d e s w t l t c h
f e a t u r e s to r e l a x a n d in w h a t o r d e r 5 a n d g e n e r a t e s a
m a s t e r o r d e r i n g of f e a t u r e s f o r r e l a x a t i o n Once t h e
f e a t u r e o r d e r Is c r e a t e d , t h e r e f e r e n c e s y s t e m u s e s
50f course, om=a one ~ r t i c u l a r candidate is selected then deciding which f e a t u r e s to relax is r e l a t i v e l y t r ( v i a l
- one simply c(mporee f e a t u r e by f e a t u r e between the candidate d e s c r i p t i o n ( t h e t a r g e t ) and the speaker's
d e s c r i p t i o n ( t h e ~ t t e r n ) and notes any d i s c r e p a n c i e s
212
Trang 10t h a t o r d e r i n g to d e t e r m i n e t h e o r d e r i n w h i c h t o t r y
relaxing the candidates
W e d r a w pr;martly o n s o u r c e s of linguistic
knowledge, pragmatic knowledge, discourse knowledge,
d o m a m knowledge, perceptual knowledge, hierarchical
knowledge, a n d trial a n d error k n o w l e d g e d u r m g this
repair process A detailed treatment of all of t h e m c a n
be found In [12, 27, 13] T h e s e k n o w l e d g e s o u r c e s are
k n o w l e d g e s o u r c e as a set of relaxation rules T h e s e
rules are written in a P R O L O G - I i k e language Figure 5
illustrates o n e s u c h linguistic k n o w l e d g e relaxation
rule This rule is motivated b y the observation in the
excerpts that s p e a k e r s typ~cally a d d m o r e important
informatlon at the e n d of a descrlpt~on (where they are
separated from the m a ~ n part of the descrlpt~on a n d
thus provided m o r e emphasis) Since the syntactic
constituents often at the e n d are relatlve clauses or
predicate complements, w e created this m o r e specdic
relaxatlon r u l e However a m o r e general a n d m o r e
applicable rule is that information p r e s e n t e d at the
e n d of a descrlptlon is usually m o r e p r o m m e n t
R e l o x t h e f e a t u r e s i n t h e s p e a k e r ' s d e s c r i p t i o n i n t h e
o r d e r : o d j e c t i v e s , t h e n I : r e p o e i t i o n o ! p h r o e e e , o n d
f i n o l l y r e l c t i v e ¢ l o u s e s o n d p r e d i c c t e c o m p l e m e n t s
E g
Rel o x - F e o t ure-Be f o r e ( v 1 v 2 )
< - O b j e c t O e e c r ( d ) ,
Feat ureOeec r i p t o r ( v ! ) ,
FectureOescr iptor(v2),
FecturelnOeecr i pt i o n ( v f d )
Feat u r e l nOesc r i pt i on(v2 d )
5"quo I ( s y n t o c t i c - f orm(v t d ) , " A D J " )
;'quo I ( s y n t a¢t i c - f o r m ( v 2 d ) , "REL-CLS")
Figure 5: A sample relaxation rule
E a c h k n o w l e d g e s o u r c e p r o d u c e s ~ts o w n partial
o r d e r m g of features T h e partial o r d e r m g s are then
perceptual k n o w l e d g e m a y say to relax color However
~f the color value w a s asserted ~n a relative clause
linguistic k n o w l e d g e would r a n k color lower ~.e
p l a c m g ~t later ~n the list of things to relax
S m c e different k n o w l e d g e sources generally have
d i f f e r e n t p a r t i a l o r d e r l n g s of f e a t u r e s , t h e s e
d i f f e r e n c e s c a n l e a d to a c o n f l i c t o v e r w h i c h f e a t u r e s
to r e l a x It Is t h e j o b of t h e b e s t c a n d i d a t e a l g o r i t h m
to resolve the d~sagreements a m o n g k n o w l e d g e sources
It's goal ts to order the referent candidates, Ci, so
that relaxation ~s a t t e m p t e d o n the best candzdates
first Those candidates are the ones that c o n f o r m best
to a p r o p o s e d feature ordering To start, the algorithm
e x a m m e s pairs of candidates a n d the feature order~ngs
from e a c h k n o w l e d g e source For e a c h candidate C i
speaker's orlglnal descrlpt~on to C i using the feature
ordering from o n e k n o w l e d g e source T h e score
reflects the goal of mln~mlz:ng the n u m b e r of features
relaxed whale try3ng to relax the features that are
"earhest" sn the feature o r d e r m g It repeats ~ts
scoring of C i for e a c h k n o w l e d g e source, a n d s u m s u p
its scores to form Ci's total score T h e Ci's are then
o r d e r e d by that score
Figure 6 provides a graphic description of th~s
selected by the partial m a r c h e r as potent~a| candidates
f o r t h e r e f e r e n t T h e s e c a n d i d a t e s a r e s h o w n a c r o s s
t h e t o p of t h e f i g u r e The l i n e s on t h e r i g h t s i d e of
describe that object T h e speaker's descrlpt~on ts
r e p r e s e n t e d in the center of the figure T h e set of
s p e c i f i e d f e a t u r e s a n d t h e i r a s s i g n e d f e a t u r e v a l u e (e.g., t h e p a i r C o l o r - M a r o o n ) a r e a l s o s h o w n t h e r e A
s e t of p a r t i a l o r d e r i n g s a r e g e n e r a t e d t h a t s u g g e s t
w h i c h f e a t u r e s i n t h e s p e a k e r ' s d e s c r i p t i o n s h o u l d be
r e l a x e d f i r s t - o n e o r d e r i n g f o r e a c h k n o w l e d g e s o u r c e ( s h o w n as "l~nguist~c," "Perceptual." a n d "H~erarchlcaI"
in the figure) T h e s e are put together to form a directed g r a p h that represents the possible, reasonable
w a y s to relax the features specified tn the s p e a k e r s
r e o r d e r e d using the information e x p r e s s e d ~n the speaker's description a n d in the directed g r a p h of
f e a t u r e s
OQ/ecrl
• *a p m - c ~ a l FI -~ ¢o1¢*- f~ t l oe fz P~
¢ - ) N|eeet.¢tnlceJ f3 - ) F ~ I : I ~ f2 F3 fZ oe f~ oe F,*
f4
5
O~Nct4d C t ~ of/~rtu.s I ~ ,*~,~r~;~
Figure 8: Reordering referent candldates
O n c e a set of ordered, potential candldates are selected, the relaxation m e c h a n l s m b e g m s step 3 of relaxatlon; it trles to find p r o p e r relaxation m e t h o d s to relax the features that h a v e lust b e e n o r d e r e d ~success
tn flndlng s u c h m e t h o d s "justifies" relaxing the descrlptlon) It stops at the first candidate which zs reasonable
D e t e r m i n e w h i c h r e l a x a t i o n m e t h o d s t o a p p l y
Relaxation c a n take place wlth m a n y aspects of a speaker's descrlptlon: wlth c o m p l e x relatlons specified
referent specified by the descrlptlon, a n d with the focus of attention in the real world w h e r e o n e attempts
to find a match C o m p l e x relatlons speclfted in a speaker's descrlptlon include spatlal relations (e.g
"the outlet n e a r the top of the tube">, comparatives (e.g "the larger tube") a n d superlatlves (e.g., "the
longest tube") T h e s e c a n be relaxed T h e slmpler features of an object (such as slze or color) that are speclfied in the speaker's descrlptton are also o p e n to relaxation
Often the objects in focus In the real world implicitly cause other objects to be In focus [14, 2{]]
T h e subparts of a n object ~n focus, for example, are
r e a s o n a b l e c a n d i d a t e s f o r t h e r e f e r e n t of a f a z h n g
d e s c r i p t i o n a n d s h o u l d b e c h e c k e d At o t h e r t i m e s , t h e
s p e a k e r m i g h t a t t r i b u t e f e a t u r e s of a s u b p a r t of a n
213