Based on these formalizations, information and constraints to be applied to the modality analysis procedure are specified.. This analysis method has been applied to Japanese analysis for
Trang 1C L A S S I F I C A T I O N O F M O D A L I T Y F U N C T I O N A N D I T S A P P L I C A T I O N
T O J A P A N E S E L A N G U A G E A N A L Y S I S Shozo N A r r o , A k i r a S H I M A Z U , a n d H i r o s a t o N O M U R A
M u s a s h i n o E l e c t r i c a l C o m m u n i c a t i o n L a b o r a t o r i e s , N.T.T
3-9-11, Midori-cho, M u s a s h i n o - s h i , T o k y o , 180, J a p a n
Abstract
This paper proposes an analysis method for
Japanese modality In this purpose, m e a n i n g of
Japanese modality is classified into four semantic
categories and the role of it is formalized into five
modality functions Based on these formalizations,
information and constraints to be applied to the
modality analysis procedure are specified T h e n by
combining these investigations with case analysis, the
analysis method is proposed This analysis method has
been applied to Japanese analysis for machine
translation
1 I n t r o d u c t i o n Since the m e a n i n g of a sentence consists of both
proposition and rnodality, TM analysis of modality is as
indispensable as that of proposition for natural
language understanding and machine translation
H o w e v e r studies on natural language analysis have
mainly concerned with t h e propositional part, and
algorithms for analyzing rnodality have not yet been
sufficiently developed T h e aim of this paper is to
clarify the function of modality and to propose a method
for analyzing the modality in Japanese sentences
Structure of a Japanese complex sentence can be
formalized roughly by iterative concatenation of simple
sentences The simple sentence consists of cases and a
predicate The cases have surface representations of
noun phrases or adverb phrases while the predicate has
that of verb or adjective or adjective verb A noun
p h r a s e is d e f i n e d as the r e c u r s i v e c o n c a t e n a t i o n of noun
p h r a s e or t h a t of e m b e d d e d s e n t e n c e We have
e m p l o y e d '.he case s t r u c t u r e as a basic m e a n i n g
s t r u c t u r e for a s i m p l e s e n t e n c e , and e x t e n d e d it to
r e t a i n the c o n s t r u c t i o n of complex s e n t e n c e s
m e n t i o n e d M o d a i i t y is a d d i t i v e i n f o r m a t i o n
r e p r e s e n t e d by a u x i l i a r y words such as m o d a l p a r t i c l e s ,
e n d i n g p a r t i c l e s , a n d a u x i l i a r y v e r b s a n d s e n t e n c e
adverbs The m o d a l p a r t i c l e is a t t a c h e d to a noun
p h r a s e or a s e n t e n c e e l e m e n t while the e n d i n g p a r t i c l e
is a t t a c h e d to the enci position of a s e n t e n c e The
a u x i l i a r y verb ! m m e d i a t e l y follows a v e r b p h r a s e
M o d a l i t y r e p r e s e n t e d in such g r a m m a t i c a l l y d i f f e r e n t
context is incorporated into the case structure, and the
result construction is n a m e d as an extended case
structure Ivl which enable us to propose a uniform framework for analyzing both proposition and modality
In this paper, we first classify modality into four semantic categories Second, we define five modality functions using the logical representation of the
m e a n i n g and then characterize the roles of each function Third, we specify hard problems to be resolved in modality analysis Fourth, we list the information and constraints to be considered in establishing the procedure of modality analysis Then,
we propose a method for analyzing modality based on these investigations Finally, we exemplify the analysis by showing translations from Japanese into English The method has been used to analyze Japanese sentences in a machine translation system 17~
2, Classification of modality Traditionally, modality has been classified into three categories, i.e tense, aspect and modal :0-! This classification is not sufficient for the deep analysis of the m e a n i n g structure of a sentence, however, because
it does not account for the role of Japanese modal particles Adding t h i s role, we expand this
c l a s s i f i c a t i o n into four c a t e g o r i e s , n a m e l y tense, aspect,
modal a n d implicature s h o w n in T a b l e 1 E a c h c a t e g o r y can be f u r t h e r c l a s s i f i e d into s u b c a t e g o r i e s , and those
a r e shown in T a b l e 2 t h r o u g h T a b l e 5 ( E a c h t a b l e g i v e s both e x a m p l e s of J a p a n e s e e x p r e s s i o n s a n d t h e i r
E n g l i s h e q u i v a l e n t s ) O u r c l a s s i f i c a t i o n of m o d a l i t y
f e a t u r e s two c h a r a c t e r i s t i c s c o n c e r n i n g the a s s i g n m e n t
of a d v e r b s a n d m o d a l p a r t i c l e s : (1) A m o n g the two k i n d s of a d v e r b s , n a m e l y
s e n t e n c e a d v e r b s a n d case a d v e r b s , we a s s i g n
s e n t e n c e a d v e r b s to m o d a l i t y while case
a d v e r b s to case r e l a t i o n s S e n t e n c e a d v e r b s a r e classified into t h r e e s u b c a t e g o r i e s in the m o d a l
Table I Four categories of Modalitv
Tense i temporal view of a event relative to the speaking
time state of events viewed from time progress at a Aspect sl:ecifled time point
Modal speaker's or agent's attitude or judgement to the
occurrence of events implicative meaning represented by modal
I mplicature particles
Trang 2category : [evaluation], [judgement] a n d
adverbs are assigned to modality.)
(2) M o d a l particles are assigned to modality a n d
implicature (They h a v e been usually discussed
separately from modality) ~41
3 M o d a l i t y functions a n d their roles
representation of the m e a n i n g structure, w e can define
modality functions as operations on logical expressions
analysis in logical f r a m e w o r k treated each type of
modality individually IsH6] Here, w e deal with it,
however, as a w h o l e a n d c o m b i n e it with the
propositional structure so that w e can provide a
uniform f r a m e w o r k for the representation a n d the
analysis of the m e a n i n g structure In this purpose w e
e m p l o y the higher order m o d a l logic formalism It1
In this regard, w e introduce the five types of
modality functions, w h i c h add or modify modality :
{I) addition of the modality operator
{2) surface modification of the case structure
(3) semantic modification of the case structure
(4) determination of the scope of negation,
(5) addition of the implicative m e a n i n g
W e will n o w discuss the roles of each type of
logical representations
3.1 A d d i t i o n o f t h e m o d a l i t y o p e r a t o r
This is the m o s t f u n d a m e n t a l function a n d it simply
m e a n i n g In the following two sentences, (sl) has no
modality while (s2) has modality :
( s l ) Hiroko ga hashiru (Hiroko runs.)
Run(Hiroko),
" ~ In the ~'ollowing each example sentence is succeeded by an
English translation and a logical representation f the meaning
Japanese
English expression -ed (past tense)
present tense, or future tense (S2) Hiroko ga h a s h i t t e i r u (Hiroko is runnzng.)
[ d u r a t i v e ] R u n ( H i r o k o ) (s2) is o b t a i n e d by a d d i n g t h e d u r a t i v e aspect o p e r a t o r
" t e i r u (progressive)" to (sl) c'~
3.2 S u r f a c e m o d i f i c a t i o n o f t h e c a s e s t r u c t u r e
T h i s does n o t c h a n g e the logical m e a n i n g s t r u c t u r e
e v e n w h e n the surface s t r u c t u r e is modified H o w e v e r
h i g h e r level i n f o r m a t i o n such as focus a n d a t t e n t i o n is
s o m e t i m e s added
T h e passive a u x i l i a r y v e r b " r e r u " or " r a r e r u " c a n modify the surface case s t r u c t u r e w i t h o u t c h a n g i n g the logical m e a n i n g s t r u c t u r e T h e focus is u s u a l l y placed
on the ~ubject p a r t of the passive s e n t e n c e , as follows : (s3) Hiroko ga y a s a i we t a b e r u
(Hzroko eats vegetables.},
3x(Vegetable(x)AEat(Hiroko,x)), (s4) Yasai ga Hiroko ni tabe rareru
(Vegetables are eaten by Hzroko.),
3x((Vegetable(x)AEat(Hiroko,x))A{Focus(x)}),
w h e r e the predicate Focus(x) signifies that the focus is placed on the a r g u m e n t x
3.3 S e m a n t i c m o d i f i c a t i o n of the c a s e structure This results in one of the two alternatives : (a) one a r g u m e n t is a d d e d to the original predicate, (b:, a higher order predicate is introduced
Both changes are equivalent in m e a n i n g but the w a y of representing the c h a n g e is different
semantic modification of the case structure : I) causative C s e r u " or "saseru"), 2J affected-passive C r e r u " or "rareru"), 3) hope Ctehoshii'" a n d "temoraitai"), 4~ request ,~"temorau"),
5) benefit ("tekureru teageru", a n d "teyaru") Tabie 2 Aspect ( tdou means c o n c a t e n a t i o n , and d~ mtans empty character.)
Inchoative
• ust-bei'or e- incJ'd~a tive
haji mf~ru, - kakeru ~dasu
I ( - h a j i m e r u , *-kakc:u ~dasuJ (tokoro, bakari;, u~.osuru, tokoro, bakari
[inchoa=ive verhl begin, commence, start: 'set about - -ing' fai to c~me to, take to
I be go ng to be go=ng to-*-[inchoative verbl just have [inchoative verbi-en
J u s t - a f t e r d n c h o a t i v e i - - h a ' l i n e ~ k a k e ~ d a s h i # ta - ( t o k o r o , h a k a r i )
Durative ~teiru, ~ e.ru, ~tsuLukert:, ~tesrutokoro, 11dut-:ttive verb~ go on, "keep (onJ *- -ing' continue, remain,
Terminative
J ust-before-termin:, te
owaru, oeru, -teshimau (-owaru, -oeru, -teshimau) - (tokoro, bakarD (-owat, -oe, ~teshimat, d#) ta- (tokoro, bakari)
! ~owat, -oe, te.~himat, ~b) • telru
J ust-after-terminative
Terminative- qtate
I
{affected verbl cease, finish, leave off, discontinue, 'stop d- -ing'
be going t.o -¢- { affected verbl
[ just have {affected verbl-en
i huve-,~ en
Trang 3F o r a n e x a m p l e , the c a u s a t i v e a u x i l i a r y v e r b " s e r u "
or % a s e r u " r e s u l t s in (a) the a d d i t i o n of the c a u s a t i v e
a g e n t , or (b) t h e i n t r o d u c t i o n of a s e c o n d - o r d e r
p r e d i c a t e C A U S E ( x , y ) in w h i c h a r g u m e n t x r e p r e s e n t s
the c a u s a t i v e a g e n t a n d a r g u m e n t y r e p r e s e n t s a
p r e d i c a t e , as follows :
(s5) T a r o ga H i r o k o ni y a s a i wo tabe s a s e r u
(Taro makes Hiroko eat vegetables.)
( a ) 3 x ( V e g e t a b l e ( x ) / ' , E a t ' ( H i r o k o , x , T a r o ) ) , or
( b ) 3 x ( V e g e t a b l e ( x ) A C A U S E ( T a r o ,
Eat(Hiroko,x))),
w h e r e t h e p r e d i c a t e E a t ' ( x , y, z) is o b t a i n e d by a d d i n g
the a r g u m e n t z c o r r e s p o n d i n g to the c a u s a t i v e a g e n t to
the p r e d i c a t e Eat{x, y) in (s3)
F o r a n o t h e r e x a m p l e , t h o u g h the a u x i l i a r y v e r b
" r e r u " or " r a r e r u " has five m e a n i n g s , n a m e l y ,
"passive", "affected-passive", " a b i l i t y " , " r e s p e c t i v e " and
" s p o n t a n e i t y " , " p a s s i v e " m e a n i n g a m o n g t h e m falls
into type (2) above w h i l e " a f f e c t e d - p a s s i v e " m e a n i n g
falls into this type and the a f f e c t e d - a g e n t is added :
Is6) T a r o ga H i r o k o ai y a s a i wo tabe r a r e r u
(Taro was'adversely) affected
by Hiroko's eating vegetables.)
(a) 3x(Vegetable( x }/xEat"(Hiroko.x.Ta ro)), or
( b ) 3 x ( V e g e t a b l e ( x ) A A F F E C T E D - P A S S I V E
( T a r o , E a t ( H i r o k o , x ) ) ) 3.4 D e t e r m i n a t i o n o f t h e s c o p e o f n e g a t i o n
Meaning
Limitation
D e g r e e
Extreme-example
Japanese expression shika, kin, dake, bakari, made, kurai
sac, demo, datte, m a d e
English expression only
as, about
e v e n
T h e m o d a l p a r t i c l e " w a " d e t e r m i n e s the role of the
a u x i l i a r y v e r b " n a i " as a p a r t i a l n e g a t i o n w h i l e the case
p a r t i c l e " g a " d e t e r m i n e s it as total n e g a t i o n In t h e
f o l l o w i n g s e n t e n c e s , (s9) is p a r t i a l l y n e g a t e d w h i l e (s8)
i s t o t a l l y n e g a t e d : (s7)Zen'in ga k u r u [Everybody comes.)
v x ( S ( x ) 3 C o m e ( x ) ) , (s8)Zen'in ga ko nai (Nobody comes.)
vx(S(x) ~ ~ Come(x)), (sg)Zen'in wa ko nai (Not everybody comes.)
v x ( S ( x ~ ~ C o m e ( x ) ) ,
w h e r e the p r e d i c a t e S(x) d e n o t e s " z e n ' i n [all the persons)"
Table4 Medal
rareru
can he able to
be possible
hougayoi
I nikoshitakotohana
Try
! C o m m a n d Question
nasal, [imperative form of verbl
ka
English expression try
[imperative form of verbl
transformationl
(to 2nd personl
I s e r e s a s e r u
Causation
Certain-presumption !hazuda nichigainai must
t o o m ( ~ w a r e r u
int.ention , u, :sumortda utoshiteiru be going to will
kotonishiteiru
make (a person, ',, do get (a person~ to do have
{passive transformationl [affected-passive
•
d e s u , m a s u
P o l i t e n e s s
Respect Evaluationl
r e r u r a r e r u
saiwalnimo,
z a n n e n n a k o t o n i
o d o r o i t a k o t o n i
akirakani, o m o u n i
genmitsuniitte,
hontounotokoro
fortunately, regretably,
to our surprise perhaps, surely, evidently,
in m y opinion
i n s h o r t
strictly speaking,
in all fairness
Trang 43.5 A d d i t i o n o f t h e i m p l i c a t i v e m e a n i n g
An extra logical formula corresponding to the
implicative m e a n i n g is added by modal particles such
as % h i k a (onlyf and ~dake (only)" as in :
(sl0) Hiroko w a yasai shika tabe nai
(Hiroko eats nothing but vegetables.)
~x(Vegetable(x)AEat(Hiroko,x))
4, P r o b l e m s in modality analysis
4.1 A m b i g u i t y of the modality m e a n i n g
(I) Ambiguity due to multiple m e a n i n g
The aspect expression "teiru" has three different
kinds of meanings, that is, the "durative", "iterative" or
"terminative-state" aspects For example,
(sll)Hiroko ga yasai w o tabe teiru
(Hiroko {is eating, eats and eats has eatenl
vegetables.)
3x(Vegetable(x)
/x{[durative],[iterative],[ t e r m i n a tire-state]}
Eat(Hiroko, x))
(21 Ambiguity concerned with case structure
As stated in Section 3.3 above, the auxiliary verb
"reru" or " r a r e r u " has five meanings, and, among them,
the "passive" and "affected-passive" meanings result in
disambiguation of the m e a n i n g of ~reru" or " r a r e r u "
has a close relationship to analysis of the propositional
meaning
Moreover the auxiliary verb " r a r e r u " in the
following {s12) means "respect", and that in (s13)
expressions are same except the additional m e a n i n g of
respect and focus, as follows :
(sl2)Sensei ga yasai w o tabe rareru
(The teacher eats vegetables.)
3x(Vegetable(x)/kEat{the-Teacher,x))
ARespect(Speaker,the-Teacher), (sl3)Yasai ga sensei ni tabe rareru
(Vegetables are eaten by the Teacher.;
3x((Vegetable(x)/xEat(the-Teacher,x))
/x{Focus(x)}), where the predicate Respect{x,y) m e a n s that x respects
y
4.2 S c o p e of modality
does not always m e a n that the main clause is negated
Sometimes the subordinate clause is negated W e call
Furthermore even if rnodality involved is not negation,
it sometimes affects the subordinate clause
Although the main clause in the following (s14) is
not usually negated, the subordinate clause is
Nevertheless, the tense information in the m a i n clause has an effect on the subordinate clause (s14) is constructed from (s14-1) and (s14-2) by a simple coordinate conjunction, however the corresponding logical expression is not a simple concatenation of each
(sl4)Taro w a hige w o sot be kaisha e ika nakat ta
(Taro went to the company without shaving.)
[past] Shave(Taro,beard)
A{past]Go(Taro,Company),
Shave(Taro, beard), (sl4-2)Taro wa k a i s h a e ika n a k a t ta
(Taro did not go to the company.) [past] Go(Taro, Company)
(sS) and (s9) also exemplify the problem for determining the scope of negation
4.3 T r e a t m e n t of implicative m e a n i n g
Modal particles such as "shika (only)" and "sae
order to obtain the logical representation of the implicative meaning, we are forced to provide different formulae expressive of the each m e a n i n g of each modal particle For example, if w e assign the formula (fl) to the expression %hika nai" which consists of the modal particle "shika" and auxiliary verb "nai", w e get the logical representation of the sentence Is10) by the
AVx(-,P(x)~R Q(x)))
the implicative m e a n i n g is very individual This concludes that specification of it for each m e a n i n g is
is therefore needed
5 I n f o r m a t i o n a n d c o n s t r a i n t s on m o d a l i t y
a n a l y s i s (1) l,exicai m e a n i n g The lexical m e a n i n g assigned to each modality expression is the most fundamental information So w e need to specify and provide it For example, the lexical meaning of the auxiliary verb "ta" is generally the
"past" tense as in :
(slS)Hiroko ga hashit ta (Hiroko ran.)
[past]Run(H.;roko)
(2) Predicate features Predicate features are available for disambiguating the m e a n i n g of modality
T h o u g h the aspect auxiliary verb "teiru" is ambiguous in meaning, w e can resolve it by using predicate features such as the "stative", "continuous" and "spontaneous", as in :
Trang 5( s l 6 ) H i r o k o ga h a s h i t t e i r u (Hiroko is running.)
[ d u r a t i v e ] R u n ( H i r o k o ) ,
( s l 7 ) A k a x i ga kie t e i r u (The light is turned off.)
[ t e r m i n a t i v e - s t a t e ] T u r n - o f f ( t h e - L i g h t ) ,
where the verb mnashiru (run)" h a s the " c o n t i n u o u s "
f e a t u r e while the verb " k i e r u (turn off)" h a s the
" s p o n t a n e o u s " feature T h e aspect expression " t e i r u "
following a " c o n t i n u o u s " verb u s u a l l y m e a n s the
" d u r a t i v e " aspect, a n d " t e i r u " following a
" s p o n t a n e o u s " verb u s u a l l y m e a n s the " t e r m i n a t i v e -
state" aspect
T h e " s p o n t a n e i t y " m e a n i n g of " r e r u " or " r a r e r u " is
realized o n l y w h e n it follows the v e r b s h a v i n g
s p o n t a n e i t y feature such as "omoidasu (remember)" a n d
" a n j i r u (care)"
(3) N o u n p h r a s e s a n d a d v e r b s
Some k i n d s of n o u n phrases, adverbs, a n d t h e i r
s e m a n t i c categories can be utilized to d i s a m b i g u a t e the
m e a n i n g of modality, w h e n they occur s i m u l t a n e o u s l y
with it
( s l 8 ) H i r o k o ga yasai wo i.m.a tabe teiru,
(Hiroko is eating vegetables now.)
3x(Vegetable(x)
A [ d u r a t i v e ] E a t " ( H i r o k o , x , n o w ) )
"Hiroko" ,\PP.\QQ( HirokoJ
"yasai" \PP.\xVegetable(x}
"shika n a]" ,~.P,\Q,k R( qx( P( x )Zk R Q ( x )I
A V x ~ ~ P f x J D R ~ Q I x J J )
"taberu" ~ySzEatfz,yJ
"yasai shlka._ nai"
),PP.kx Vegetable( x hkR.\S~T( 3ul R(uJATS(uJ~
A V u ( ~ R(ul D T ~ S(u))t
- - SR.\SLT( -3u(R(uJATS( u ) ) A V u ( ", R{ u~ D T ~ S(u)~)
.\ x Vegetable( x;
\ShT( B u(.kx Vegetable( x J( u J/x.TS(u))
A V u ( ~ \x V e g e t a b l e ( x }( u~ ~ T ~ S( u J))
- - , \ S ~ T ( " ] u ( V e g e t a b l e ( u ~ A T S ( u ) JAVut -~ Vegetable(u# D T ~ S( u~)~
"yasai shika tabe nai"
S$},Tf 3u(Vegetabie(u)ATS(u))
A V u ( "- Vegetable(u) D T " S( ul)lAyAzEat(z.yl
.~T( 3tu Vegetable( u)AT,\y,kzEat(z,yi( u D
AVu( ~ Vegetable(u} DT -~ ~ykzEat(z,y fl u)}) .kTf3u(Vegetable(u)AT \zEat(z.u)l
AVu( ~ Vegetable(u)DT ~ kzEatiz u:))
"Hiroko wa yasai shika tabe hal"
.\PP.~QQ(H iroke JAT( qu( Vegetable4 uJ/\T,kzEat(z.u J)
,~,Vu, "- Vegetable( uJ DT ~ kzEat(z.uJD ,kT( =l,J(Vegetable(u}/kTSzEat(z,uU
A V u ( -, Vegetable(ul S,T -, \zEat( z,unJhPP(ilirokoj
- - ( 3 u ( V e g e t a b l e ( u l / , kPP(HirokoJkzEat(z.u)}
/ ~ V u ( ~ V e g e t a b l e ( u l D \ P P f H i r o k o J ~ ,t, zF, a ' ( z , u l ) )
( 3 u ( V e g e t a b i e ( u ~ A ~.zEat(z.ui(Hiroko))
AVu( Vegetable( a J D " kzEat( z,u}( I I irokol)J
~ ( ~ u ( V e g e t a b l e ( u t / k E a t ( I l i r o k o , , , ) J '
AVu( ~ Vegetable(u) D "~ Eat( Hiroko,ulD Fig 1 Logical analysis of the setltence (sl0)
(s19)Hiroko ga y a s a i wo s u d e n i tabe t e i r u
(Hiroko has already eaten vegetable.)
3 x ( V e g e t a b l e ( x ) A [ t e r m i n a t i v e - s t a t e ]
E a t ' ( H i r o k o , x , a l r e a d y ) )
I n the above e x a m p l e s , the a d v e r b " i m a (now)" is
c o n c e r n e d w i t h the " d u r a t i v e " aspect, w h i l e " s u d e n i
(already)" is c o n c e r n e d w i t h t h e " t e r m i n a t i v e - s t a t e " aspect T h e a r g u m e n t z of the predicate Eat"'(x,y,z)
r e p r e s e n t s time i n f o r m a t i o n
(4) M o d a l p a r t i c l e s
As discussed i n Section 3 ( s e n t e n c e s (s8) a n d (s9)), the modal particle "wa" o c c u r r i n g s i m u l t a n e o u s l y w i t h
n e g a t i o n s u g g e s t s p a r t i a l n e g a t i o n
(5) C o n j u n c t i v e r e l a t i o n s
C o n j u n c t i v e r e l a t i o n s are r e l a t e d to the scope of
m o d a l i t y If the s u b o r d i n a t e clause has the following
c o n j u n c t i v e r e l a t i o n s r e p r e s e n t e d by (a) the c o n j u n c t i v e particle "te", or (b) a r e l a t i v e n o u n such as "toki (trine)" or "mae
the t r a n s f e r of n e g a t i o n can be predicted as in s e n t e n c e (s14) O t h e r w i s e , the t r a n s f e r will n e v e r occurs as follows :
(s20)Taro wa hige wo sot ta ga
k a i s h a e ika n a k a t ta
( T h o u g h Taro s h a v e d his beard,
he did not go to the company.) [ p a s t ] S h a v e ( T a r o , b e a r d )
A[ past] ~ G o ( T a r o , C o m p a n y ) (6) S e m a n t i c r e l a t i o n s b e t w e e n t h e s u b o r d i n a t e
c l a u s e a n d t h e m a i n c l a u s e
T h i s i n f o r m a t i o n is used to d e t e r m i n e the scope of
n e g a t i o n in the m a i n clause In the s u b o r d i n a t e clause with the c o n j u n c t i v e particle "te", if the e v e n t expressed
by it is s u b s i d i a r y for the occurrence of the e v e n t in the
m a i n clause, the t r a n s f e r of n e g a t i o n can occur O n the other h a n d , if the s u b o r d i n a t e e v e n t is i n d i s p e n s a b l e to the occurrence of the m a i n e v e n t , the t r a n s f e r n e v e r occurs For example, in (s14), since the modifier e v e n t
S h a v e ( T a r o , b e a r d ) is a s u b s i d i a r y e v e n t for the occurrence of the m a i n e v e n t Go(Taro,Company), the
t r a n s f e r of n e g a t i o n is possible In the following
s e n t e n c e (s21), however, since the e v e n t Go(Taro,
W a s h i n g t o n ) is a n i n d i s p e n s a b l e e v e n t for the occurrnece of the m a i n e v e n t See(Taro,White-House), the t r a n s f e r ts impossible :
(s21)Taro wa W a s h i n g t o n e it te
W h i t e House wo mi n a k a t ta
(Taro did not see the White House
when he went to Washington.)
[ p a s t ] G o ( T a r o , W a s h i n g t o n ) A[past] -, S e e ( T a r o , t h e - W h i t e - H o u s e )
Trang 66 M o d a l i t y a n a l y s i s 6.1 S t r a t e g y o f t h e m o d a l i t y a n a l y s i s
Considering the five modality functions defined in
Section 3, it is a p p a r e n t t h a t the logical analysis
method alone is not effective for modality analysis
There are three reasons for this :
(1) Reference to other expressions is needed to
resolve the a m b i g u i t y of the modality function,
(2) Structural modification occurs when the scope
of negation is transferred,
(3) Analysis of the implicative m e a n i n g sometimes
cause the change of logical expression
There remains, however, the problem of taking the
individuality of each modality into account For some
kinds of modality, the result of the case analysis or the
represent the reasons why we propose an analysis
method consisting of the following three modules
combined with the case analysis and the conjunctive
analysis :
( 1)pre-case-analysis :
activated before the case analysis,
(2)post-case-analysis :
activated after the case analysis,
(3)post-conjunctive-analysis :
activated after the conjunctive analysis
The relationship of these three modules to the case
analysis and the conjunctive analysis is s h o w n in Fig
2
ore-case.analysis :
f [ case analysis ]
post-case-analysis : [
(I} disambiguation of the modality function [
E (2) (31 addition determination of the scop~ of negation of the implicative meaning [
I c°njunctive analysis I post-conju nctive-an alysis :
I determinatioa of the scope of the modality
in the main clause Fig 2 Framework of the m,dality analysis
6.2 A l g o r i t h m s of e a c h sub-analysis
(1) Pre-case-analysis
T h e modality whose analysis requires only lexical
m e a n i n g or which causes a change of the case structure
is analysed at this stage T h e case frame to be assigned
to the predicate is mcdified by utilizing the result of
this analysis before starting the case analysis A s for the semantically a m b i g u o u s auxiliary verb "reru" or
"rareru", its role is only predicted at this stage, because
it is also concerned with the modification of the case structure After case analysis, the plausibility of the prediction is evaluated T h e modification of the case frame is as follows :
(a) For the "passive" m e a n i n g of "reru" or "raxeru" (which causes a surface change to the case structure as mentioned in Section 3.2), the object case of the original case frame is changed into the surface subjective case, and the modality category "passive" is assigned to the m e a n i n g structure If two object cases exist, two possible modifications are performed
(b) With the modality causing a semantic change to the case structure (for the modality function stated in Section 3.3), a n e w case is added as follows:
(bl)For the "causative", "affected-passive",
"hope" or "request" m e a n i n g : A n e w agent (e.g causative-agent / affected-agent) is added, and the case particle of the original subjective case is changed from "ga" to "hi",
(b2)With the "benefit" m e a n i n g : A beneficiary case is added T h e case particle in this case is
"hi"
Also the modality category corresponding to each m e a n i n g (e.g "causative", "affected- passive") is assigned to the m e a n i n g structure
(2) Post-case-analysis
T h e modality whose analysis requires case structure information is analyzed at this stage This module determines the function of the modality as follows : (a) [f the category of the modality expression is unique, this category is assigned to the m e a n i n g :;tructure
(b) if a d a e m o n (a procedure to resolve ambiguities
by using heuristics) is attached to the rnodality expression, it performs the three tasks :
(bl) disambignating the function of the modality expression,
(b2) detcrmining the scope, (b3) adding the implicative meaning
The d a e m o n utilizes the information mentioned in (I) - (4) in Sect, ion 5 For example, a d a e m o n attached to the aspect expression "teiru" works as s h o w n in Fig 3 (3) Post-conjunctive-analysis
Following the conjunctive analysis between the subordinate clause and the m a i n clause, this module is activated to determine whether the modality in the
m a i n clause also operates on the subordinate clause This module utilizes heuristics consisted of all of the
Trang 7Is there a case element (noun phrase or adverb) suggesting
"terminative-state" or "durative" or "iterative" aspect? [
no Does "teiru" follow
" r e r u " o r ~rarerxl'~
yes ~,
I terminative-
state aspect
[ terminative-state [
[ or durative
~no [ or iterative aspect
I Is the feature of the predicate
"spontaneous~ I
Fig 3 Daemon which disambiguates the meaning of
the aspect expression "teiru"
information presented in Section 5 A n example of
heuristics which analyze the scope of the a u x i l i a r y verb
"ta" is shown in Fig 4
For n e g a t i o n in the m a i n clause, the transfer of
n e g a t i o n is considered W h e t h e r or not the modifier
event is subsidiary for the occurence of the m a i n e v e n t
is tested using the s e m a n t i c relations assigned to the
)redicate of the m a i n clause
Is conj unction of the subordinate clause conjunctive
particle "te" "to" "ba n or "renyou~chuushi"?
and Does the subordinate clause have time information
such as time cases?
operate time ir~'ormation in the main ~ I no operation I
clause over the subordinate clause
Fig 4 Heuristics which analyse the scope
of the auxiliary verb "ta"
6.3 Application to J a p a n e s e analysis
(I) E x t e n d e d case analysis
W e have already proposed a method n a m e d
extended case analysis for Japanese sentences IvT Input
to the extended case analysis is an ordered list of word
frames produced by a morphological analysis The
analysis begins to predict a constituent construction of
the sentence to be analyzed by utilizing syntactic
structure patterns, and then enter into the detail
analysis of semantic relations between pairs of the
modifier and the modificant by utilizing semantic
relation frames There are four types of the semantic
relations, namely, case relation, noun concept relation,
embeding relation and conjunctive relation All of
these semantic relations are analyzed in a uniform
framework The both analyses go on iteratively and/or
recursively from a small chunk of constituents to large
one Each iteration and recursion executes both the
prediction of the syntactic structure and the analysis of
semantic structure The modality analysis is
incorporated into those processes
Let us show the modaiity analysis process for the
following example sentence :
(s22)Niku wa n o k o t teite,
y a s a i d a k e ga K i r o k o ni tabe rare teita
Meat had remained, and only vegetables had been eaten by Hiroko
At first, it is a n a l y s e d t h a t this sentence is a complex sentence by utilizing s y n t a c t i c s t r u c t u r e p a t t e r n s
A f t e r s e m a n t i c s t r u c t u r e s of the modifier and the m a i n clause are analysed, conjunctive relation between these clauses is analyzed Now, we show a n a l y s i s of the m a i n sentence
T h e following case e l e m e n t s a n d a predicate are analysed by applying structure patterns before starting case analysis :
case1 = "yasai", "ga", "dake", case2 = ~liroko", "ai", predicate = "taberu", "rareru", %eiru", %a', where "dake", "rarern', "teiru", and "ta" are modality exp~'essions "Hiroko" and "yasai" have semantic categories, [human] and [food] respectively in each word frame
(2) Modification of case f r a m e Case frame is prepared for each m e a n i n g of each predicate A n intrinsic case frame for the verb "taberu
(eat)" is as follows (Optional cases such as time and place are omitted here) :
[the intrinsic case frame of the verb "taberu (eat)"] :
Agent [human], "ga", Object = [food], ~wo"
Each case slot in the case frame is assigned semantic categories and case particles as constraints to be satisfied by the filler
The following alternative case frames produced by modifying the intrinsic frame are also prepared before starting case analysis because of the existence of the
a u x i l i a r y verb ~rareru" : ["passive" modification of the case frame] :
A g e n t = [ h u m a n ] , "hi", Object = [food], "ga", ["affected-passive" modification of the case frame] : Affected-agent - [ h u m a n ] , "ga",
A g e n t = [ h u m a n ] , "ni", Object - [food], "wo"
These three case frames are examined w h e t h e r each case e l e m e n t in the sentence satisfies constraints As a result, in this case, "passive" modification case frame is selected as a best m a t c h i n g , and case role of each case
e l e m e n t is d e t e r m i n e d as follows :
c a s e l = Object, case2 = Agent
This result is showing that the m e a n i n g of ~rareru" is
"passive"
(3) Determination of meaning of modality
Modality by modal particles in case elements a n d attxiHary verbs are analyzed A n a l y s i s of "teiru" is
Trang 8performed by the heuristics s h o w n in Fig 3, where the
m e a n i n g is determined as "terminative-state" judging
from the fact that "teiru" follows "raxeru" T h e
m e a n i n g of the modal particle "dake" is multiple, that
is, "limitation" and "degree" In this case, "limitation"
(4) Determination of scope of modality in the m a i n
c l a u s e
After conjunctive analysis between the modifier and
the m a i n clause, scope of the auxiliary verb "ta" in the
m a i n clause is analyzed Using heuristics shown in
Fig 4, it is analyzed t h a t "ta" also o p e r a t e s on the
subordinate clause
In a result, the m e a n i n g structure of (s22) is
obtained as follows :
3x((Meat(x)A[past][terminative-state ]Remain(x))
A3x((Vegetable(x)
A[past][terminative-state]Eat(Hiroko,x))
AVx(( Vegetable(x)
~-, [pastl[terminative-state]Eat(Hiroko,x))
A{Focus(x)})
A n English sentence corresponding to this semantic
structure is s h o w n in (s22)
6.4 Virture of modality analysis
W e show contributions of modality analysis to
understanding and quality of translation for the
following example sentences
T h o u g h a t r a i n can r u n o n l y on a r a i l r o a d , the t r a i n [
s a w in a movie y e s t e r d a y c o u l d also fly
Do y o u t h i n k t h a t a train c a n fly?
(1) [speech act] As shown in (s24), modality contains
much information concerning speech act (question,
systems such as qustion answering systems, these
m e a n i n g can be used for selecting apropriate reactions
(2) [type of object] Analysis results of aspect or tense are
used for d e t e r m i n i n g the type of objects
The subordinate clause of (s23) describes a general
character o f ' d e n s h a ( t r m n ) " , and the first occurrence of
"densha" denotes a g e n e r i c object On the other hand,
the second occurrence of "denaha" is modified by an
the character of the event is analysed by the analysis of aspect or tense, the character of the objects can be specified
(3) [translation] A s s h o w n in the translated sentences
in (s23) and (s24), results of the modality analysis are clearly realized in quality of translated sentences In these sentences, modality such as "limitation",
"negation", "ability", "past", "quetion" appears
7 Conclusion
W e proposed an analysis method for Japanese
modality into four categories, and then defined five modality functions which characterize the role of
represent the m e a n i n g structure, w e could effectively
expression has the s a m e expressive power as frames or
representation can be realized by this method
Although w e dealt with the modality analysis restricted within the scope of one sentence in this paper,
on the analysis of modality in the future
W e have applied this modality analysis method to the Japanese sentence analysis in the Japanese- English experimental machine translation system, LUTE.IV!
References
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[4] Kubo, S : A Study of Japanese Adverbial Particles
in Montague G r a m m a r , "Linguistic Journal of
[5] Keenan, E : Negative Coreference : Generalizing Quantification for Natural Language, "Formal Semantics and Pragrnatics for Natural Languages",
ed by F Guenthner and S J Schmidt, 1979
[6] Nakau, M : Tense, Aspect, and Modality, "Syntax and Semantics" 5, ed by M Shibatani, 1978
[7] Shimazu, A., S Naito, and H Nornura : Japanese Language Semantic Analyser based on an Extended Case F r a m e Model, Proc of 8th International Joint