Embedding DRT in a Situation Theoretic Frmnework 
Alan W Black 
Dept of Artificial Intelligence, University of Edinburgh, 
80 South Bridge, Edinburgh EII1 tHN, UK. 
awb@ed, ac, uk 
Abstract 
This paper proposes the use of situation theory as a 
basic semantic formalism for defining general seman- 
tic theories. ASTL, a computational situation theoretic 
language, is described which goes some way to offering 
such a system. After a general description of Discourse 
Representation Theory an encoding of DRT in ASTL is 
given. Advantages and disadvantages of this method 
are then discussed. 
Topie: computational formalisms in semantics and dis- 
course 
Introduction 
Tbe pnrpose of this paper is to show how a compu- 
tational language based on situation theory can be 
used as a basic formalism ill which genera\] semantic 
theories can be implemented. There are many dif- 
ferent semantic theories which, because of their dif- 
ferent notations, are difficult to compare. A general 
language which allows those theories to be imple- 
mented within it would offer an envirolnnent where 
similar semantic theories could be more easily eval- 
uated. 
Situation Theory (ST) has been developed over 
the last ten years \[2\]. Much work has been done in 
both tlle formal aspects of situation theory and its 
use in natural language semantics (situation seman- 
tics), however so far little work has been dram ill its 
computational aspects. It is the eventual goal of 
tile work presented here to show how situation the- 
ory can be used computationally and how a com- 
putational situation theoretic language call provide 
an enviromnent ill which different semantic theories 
call I)e easily compared. 
Because there are so many variants of ST we 
must define our own here. The language ASTL \[3\] 
has been defined. Althongb it uses surprisingly 
few features of situation theory, it seems power- 
ful enough to act as a basic language for seman- 
tics. It has been considered that somc extension 
to "classical" feature structures be made and use 
those to encode semantic forms. Features systems 
augmented with set vahms, eyclicity and other ex- 
tensions may be powerful enough but the method 
described here takes an existing semantic theory 
and refines it rather than building a new one. 
This paper is ba.sically split into two sections. 
Tlw first discusses how ST can be used in a compu- 
tational system, and introduces the language ASTL. 
The second half of this paper discusses Discourse 
Representation Theory (DRT) as a theory in itself 
and shows how it can be encoded with ASTL. 
ST and Computation 
The view according to situation theory is that parts 
of the "world" can be described as situations. Sit- 
uations support facts. Facts can be true, false, or 
undefined in some situation. A fact's truth value 
may be different in different situations. Situations 
are tirst class objects in the theory, and hence they 
can be used as arguments to facts so that rela- 
tions can be defined between situations. Situations 
are useful in translations for naked infinitives (e.g. 
"see") Situations make ST different from more 
conventional logical theories although there have 
been proposals to add situation-like objects to more 
classical theories like Montagne grammar \[8\]. 
As well as situations and partiality, situation 
theory offers many other iutensional objects, in- 
cluding abstractions, types, and parameters (par- 
tially determined objects). These form a rich for- 
realism for describing semantic phenomena. How- 
ever these features alone do not constitute a com- 
putational system, with tile addition of constraints 
and rules of inference we call have the basis for 
a computatimlal system. The idea of a computa- 
tional situation theoretic language has been con- 
sidercd elsewhere. Most notable is the language 
PRosv\[' \[9\] which offers a Prolog-like language 
based on situation theory rather than first order 
logic. Other systems (e.g. \[5\]) allow the representa- 
tion of situations etc. within some other formalism 
(e.g. feature structures) but do not use situation 
theory itself as the basis for the language. 
ASTL 
ASTL is a language based on situation theory. It 
takes a very conscrvative view of situation theory, 
admitting only some basic parts. Although ASTL 
may need to be extended later, it already can be 
used to describe simple versions of semautic theo- 
ries (such ms situation semantics and DRT). Rather 
than use, or extend, PROSlT it was decided to de- 
velop a new language. ASTL includes stone built- 
ill support for natural language parsing based on 
tile ideas of Situation Theoretic Grammar \[4\] while 
PRoslrr is designed more for knowledge representa- 
tion than direct language processing. 
ASTL allows the following basic terms: 
Individuals : e.g. a, b, c. 
Parameters : e.g. X, Y, Z. 
Variables : e.g. *X, *g, *Z. 
Relations : e.g. see/2. Relation name and arity. 
i-terms : consisting of a relation, arguments and 
a polarity (0 or 1), e.g. <<sing,h, 1>>. 
AcrEs DE COLING-92, NANTES, 23-28 Ao~r 1992 1 l 1 6 PROC. OF COLING-92, NANTES, AUG. 23-28, 1992 
tylms : consisting of an abstractioll ow!r proposi 
tions. For example 
\[S ! S !~ <<aing,h,l>> 
S !~ <<aoe,h,S,l>>\] 
That is tile type of situation which supports 
the fact that h sings and h sees that situation. 
Sitnatirms : written ,as names optionally followed 
by a type. e.g. 
SI::\[T ! T !- <<rua,t,l>>\]. 
$2::\[S ! S !~ <<uee,ii,Sl,l>>\]. 
tn addition to terms there are the following sen- 
tc~tccs: 
Propositions : consisting of a situation and a 
type e.g. 
Sitl:\[S ! s !~ <<~oe,h,S,l>> 
S !~ <<dance,h,l>>\] 
Constraints : are detlncd betweell i)ropositions, 
dmy coasist of a proposition following by <= 
lbllowed by alist ofl)ropositioas. For examph~ 
Sltl:\[S ! s !~ <<happy,h,l>>\] 
<~ Sitl:\[S ! S !~ <<smile,it, l>>\]. 
The selnantics of ASTI, (delin,~d fully ill \[3\]) are de 
lined in terms of a model consisting of individuals, 
relalions, parameters, situations slid a set coasist- 
ing of pairs of situations and facts, lnfflrmally, a 
proposition is true if the denotation of the situation 
supports all of the facts in the type. A constraint is 
true if when all the propositions in the right hand 
side of the constraint are true, the left han(l prop(. 
sition is true also. As it is currently defined ASTL 
has no bailt-in delinition with respect to coherence. 
that is there is no built-in mechanism that stops a 
situation SUl)l)orting bath a fact and its dual (the 
fact with the opposite polarity) 
Coastraints can be generalised using variabh,s. 
An example will help to illustrate this. If we define 
the folh)wing basic situation and constraint: 
Sitl:\[S ) S !: <<smile,t,l>>\]. 
*S:\[S ! S != <<happy,*Y,l>>\] 
<= *S:\[S ! S )= <<smile,*Y,l>>\], 
hfforlnally the constrainl states that in ally situ 
ati(m where something smiles it. is also Imppy (m 
tlmt sanw situation). From the above bmsi(: axioms 
we can derive that tile following is true: 
Sitl:\[S ! s !~ <<happy,t,l>> 
S != <<smile,t,l>>\] 
llather than just use the linear forlns for display- 
ing ASTL objects, an extension has been added for 
OUtlmt. Based on EKN \[l\] ASTL objects can be 
displayed a.s boxes, making comple× objects nmch 
easier to view. In this notation we write situations 
its boxes with their names m a top left inset with 
facts written (in a more conventional predicate ar- 
gmnent form) inside the box. 
Using the work of Cooper \[d\] we can process 
language in a situation theoretic way. Situation 
Theoretic Grammar takes the view that utterances 
can be represented by situations. For example 
~m3 j 
"}Immko"-=~ | cat(gIT123,ProperNotm) 
/ use.of (SIT 123 ,"llartako") 
That is, the use of the phrase "llanako" gives rise 
to a situation that supports the facts that it (the 
situation) is a ProperNoun and it is a use of the 
word "Hanako". We call these utterance situaiions. 
As an utterance happens at a particular time and 
location this fact should also be recorded in the 
situation. In ASTL this temporal aspect is built- 
in to the language. A special form of constraint, 
grammar rules, can Ire used to constrain utterance 
situations~ (-;eneral constraints apply to any form 
of situation (utterance or otherwise) while gram- 
mar rules only apply to utterance situations. A 
grallilllar rllle betweea !ltLel-allce situations such a.,4 
*S:\[S ! S !~ <<cat,S,~ontonce,t>>\] 
<- *NP:\[S ! S !~ <<cat,S,NounPhra8e,l>>\], 
*VP:\[S ! S !~ <<cat,S,VorbPhrase,l>>\]. 
t;tkes into accollllt that the two utterance situations 
occm next to each other It is possible to model all 
of this within the standard constraint system by 
adding facts almut start and end l)oints of utter- 
ances (in a mmihu, way that l)C(_~s arc interpreted 
in l'roh)g) but as one of the main uses of ASTL is lan- 
guage processing it w~s felt more elllcient to buiht 
utterance situations (and constraints on them) dr- 
redly into the language. 
A basic impienmntation has been made within 
Common I,isp which takes ASTL dcscriplions (deft- 
nitions, basic situations and constraints) and allows 
queries to be made about their sets of constraints 
and I)itsic situations. 
Discourse representation theory 
Given a simple language like ASTL there is now the 
question about }low it can be used in rel)resenting 
other semantic theories. DRT \[7\] ota~rs a represen- 
tat, ion lot discourses. A discourse rcprcsenlalion 
structure (I)RS) is dctined at each stage in a dis- 
course describing the cllrrellt state of the analys/8. 
A I)RS consists of two parts; a set of domain mark- 
rr.s, whicll can be bound to objects introduced into 
the current discourse, and a set of conditions on 
these markers. I)ltSs are typically written as boxes 
with the markers in the top part and conditions be- 
low. For example a I)RS for the utterance "a man 
81liftS" iS 
X 
=an ( X ) l_ =' 72 \] 
The following description of I)RT in ASTL is based 
on lhe I)HT definition in \[6\]. First we need a syn- 
tactic backbone to be able to discuss the construc- 
ti(m of a I)RS for a discourse. As seen (briefly) 
above AS'I'I, oilers a basic grammar formalism. That 
is, grammar rules are Sl)ecilled as eoastraints be- 
twet'n iltterance siluatiollS, 
AL'DAS DE COLING-92, NAI~'H~S, 23-28 aot~r 1992 1 I 1 7 I'ROC. OF COLING-92, NANrFs, AUG. 23-28, 1992 
Given such a backbone we need to define an 
aSTL representation for DRSs. DRSs have two 
parts. Discourse markers c0.n be represenled as pa- 
rallleters ill ASTI.. Ill situation theor3 parameters 
denote partially determined objects. Parameters 
can be anchored to other objects as information 
about tt~eir denotation is found. DRS conditions 
arc represented by i-terms. A DRS itself is repre- 
sented as a parametric situation--a situation whose 
type contains parameters. Discourse markers are 
not explicitly listed in the 1)ITS representation. An 
ASTI. representation of the I)RS for % man stags" 
is 
Sit34S::\[S ! S != <<man,X,1>> 
S != <<sing,X,l>>\] 
W\]lerl' X is a paraoleter. 
This allows a siml)le semantics close to thai of 
a conven(.ional I)RS. That is an ASTL I)RS will be 
truc Ior some situation (i.e. a model) if there exists 
an anchoring for the parameters in it which make 
it a lype of the model-situation. A special defini- 
tion will be needed for tile condition every (and 
possil)ly others if extensions to basic DI(I' are in- 
ehMed). It may be better to think of the situation 
nellie also as a parameter which gets anchored Io 
the model-sitnation. Hut as the semantics of ASTL 
relates situations names to situations (i.e. two sit- 
m~t.ion nanles can denote the same situation) flmre 
is still a level of indirection. 
DHSs arc objects which are related to utter 
anee situations. They are not themselves repre- 
sentations of the utterances but representations of 
whal tile utterances describe. 
Threading 
An iml>ortant aspect of I)RT is how a I)RS is con- 
structed from a discourse. Here (and in \[6\]) we use 
tile technique of threading. Tile general idea is that 
a DH.S gets passed through a discoarse being added 
to as the discourse l)rogresses. 
hi this description, a discourse consists of a 
set of utterance situations which call In' viewed 
tim)ugh a number of different structural relations, 
The tirsl is through tile relation daughter which 
defines tile syntactic structure of lhe discourse as 
defined by the grammar rules (immediate doini- 
nance and linear precedence). Secondly the thread 
rdal.ion defines an ordering of tile ntlerance situ- 
aliens used in the generation of the l)RSs. I,aslly 
there are two relations, range and body lined ill 
defining the logical structure of the discourse. 
The threading relation is a binary relation be- 
tween utterance situations. We will say the first 
argument is threaded to tile second. Each utterance 
situation appears exactly once a,S the second argu- 
ment in tile thread relation (i.e. il. has exactly one 
incoming thread). There is one exeeplion, a special 
situation called DStart which does not have an in- 
coming thread (it is used to represent the null con- 
text at the start of a discourse), bm does appear 
as all incoming thread for one or more utterance 
situations. There are no cycles m threadhlg but 
as we shall see there may be more than one linked 
thread of utterances within a discourse. The actual 
construction of the threading relations is discussed 
later. 
Each utterance situation is related to two DRSs, 
through tim relations DRSIn and DRSOut. A DRSIn 
DRS is tim DRSOut DRS of the incoming thread. 
Tiffs constraint can be written in ASTL o~'-; 
*S:\[S ! S !-<<DRSIn,S,*DRS,I>>\] 
<= TS:\[TS ! TS != <<thread,*Sl,*$,l>>\], 
*SI: \[S1 ! S1 != <<DRSBut,SI,*DRS,I>>\] . 
The relation between the two DRSs related to an 
utterance is also constrained, This is a core part 
of DRT. Basically the outgoing DRS contains the 
same information as the mcnming DRS plus any 
reformation the utterance adds to the discourse. In 
the cruse of a proper noun utterance situation we can 
capture this relation with the following constraint: 
*S:\[S ! S != <<DRSout,S,*DRSout:: 
*DRSlnType k 
\[D ! D !~ <<name,*X,*N,l>>\],l>>\] 
<= 
*S: \[S ! S != <<cat,S,ProperNotm,l>> 
S !~ <<uBe of,S,*N,l>> 
S != <<aem,S,*X,l>> 
S != <<DRSTn,S,*DRSin: :*DRSInType,l>>\] 
hfformation is monotonically increasing m l)RSs as 
we traverse along a thread. We are not destruc- 
tively modifying a DRS as the discourse progresses 
but constructing a new DRS which supports the 
same conditions as the incoming DRS. The con- 
straint above forms the outgoing I)RS from the 
type (*DRSInType) of tile incoming one, which will 
contain all the conditions of the incoming DRS, 
plus a new condition introducing the parameter for 
the I)roper noun and a condition on its name. 
We also have tile constraint that any argument 
or relation that appears in the conditions of a DRS 
must be related to some utterance situation by the 
relation sere previously ill that thread. This con- 
dition means that argnments are threaded before 
predicates. For example both the subject NP and 
object NP of a simple sentence will be threaded l)e- 
fore the VP. In eontrmst in \[6\] tile VP comes before 
a object NP which means a I)RS is created with 
an argmnent in a condition which is not yet deter- 
mined (i.e. a free variable). 
The other structural relations are range and 
body Each determiner utterance situation appears 
in exactly one range-relation and exactly one body- 
relation. Tile second argument to these relations 
are utterance situations that do not appear as first 
arguments in any threading relation (i.c. they are 
ends of threads). Tile DRS0ut of a determiner ut- 
terance situation is a flmction of the DRSIn I)I?~S 
plus information from the range and body related 
threads, hi the every determiner case tile DRSOut, 
constraint is 
*S:\[S ! S != <<DRSBut,S,*DRSOut:: 
*DRSInType It 
\[DS ! DS != <<every,*RangeDRS, 
*BodyDRS, l>>\] , 1>>\] 
ACRES DE COLING-92, NANTES. 23-28 AOm 1992 1 1 1 8 PROC. OF COL1NG-92, NANrrES, AUG. 23-28, 1992 
<~ 
*S: \[S ! S != <<cat,S,Doterlainer,l>> 
S != <<DRSIn,S,*DRSIn: :*DRSInTyfm,I>> 
S !~ <<aem,S,every,l>>\], 
TS : ITS ! 
TS != <<body,*S,*Body: : 
IS ! S != <<DRSOut,S,*BodyDRS,I>>\] ,i>> 
TS }= <<range,*S,*Range: : 
IS ! S != <<DRSDut,S,*RangeDRS,I>>\],I>>\] 
While for the indrtlnite determiner the DRS0ut sits- 
ply contains all the conditions from thr DRSin, 
range and body related utterances. 
*s:\[s ! s != <<DRSUot,S,*DRS0ut:: 
*DRSlnType • *DRSRType • 
*DRSBType, 1>>\] <= 
*S:\[S ! S !-<<cat,S,neter~iner,l>> 
S !~ <<DRSIn,S,*DRSln: :*DRSInType,I>> 
S != <<~em,S,some,l>>\], 
T,q: \[TS ! 
TS != <<body,*S,*Body: : 
\[IS ! S != <<DRSihlt,S, 
*\[\]odyDRS : : *DRSBType, i>>\] , I>> 
TS != <<range,*S,*Ilange: : 
\[S ! S != <<DRSIIut,S, 
*ltangeDRS : : *DRSRType, 1 >>\] , 1 >>\] . 
lhH }low is threading huilt? Thr granHnar rule~ 
sl)ecit 3' I,h(~ I)asic syntactir st, ructurc (via Ih(, 
daughl~er relations). At, the same tim(' the thread 
ilig inforlllatioll can be COllStrllCLl!d. Each ilttl!rallc(! 
situation is related to I, wo others I)y (lie relations 
need mid out. Th(! need r(!Iation id('ntities tJ.' ut 
teranc( situation (either itself or on( of its daugh- 
ters) which requires an interning tin'end while out 
identifies which situation is to be threaded on to the 
next part of the discourse. AIIhough th( need and 
out relations are determined al the tillle a grall/- 
ill~tr rule is realised the :-tetllaI t:hread, range and 
body relations Inay not be detrrmined locally. The 
utterance to be threaded to the need of an NP can 
not Ire realised until thr NI ) is put in context tn 
contrast with \[6) inslea(I of i)assing up the utter 
ante that needs a Ihrrad, they i)ass down the "hi 
t.erance" that is to be tlu'('a(led in. lh're w(' giv(' 
a }>ottolll tip definition rather 1111111 ~1.¢; ill \[(i\] a lop 
(\[own OIle. 
As seen ill the (Ollstraillts above Ill(' strtlctural 
\[a('ts whose relations are thread, range and body 
ar(~ colhx:t,ed in a siUiation called TS tlelow is an 
(!xanlp\[(! sent, eiicc showa ;is a sylll,ax tree willl the 
thread relation dr~twn as arrows to show the flow 
of information through the disconrs(~ 
D 
,* ,nan like,~ ll.),.ko 
in adclition, DStart is threaded to D, N and NP2. 
The main discourse thread will go throngh D. There 
are two other threads ending at NP1 and S. D will be 
related to NP1 by the relation range and to S by the 
relation body, llence th(~ output DRS from the sen- 
tence (from the determiner "a" by the constraints 
given shove) is built from tile incoming l)tkq plus 
lhe outgoing l)}lSs from NP1 and S (which are re- 
lated to I) via the range and body relations). 
Pronouns and Accessibility 
Unlike other utterance sitmttions, pronouns do not 
just add new information to a I)RS. They also re- 
quire existence of sonre referent already introduced 
in the context, qb put it simply there must be a 
suitable object m the incoming I)RS that the pro- 
IIOIIn C;MI II/~LLch. A (:oil(lition can |re written ;L~ 
*S: \[S S !" <<DRSout,S,*DRSout: : 
*DII.S InType • 
\[DS ! DS != <<is)*X,*Y,I>>J,I>>\] 
*S:(S S != <<cat,S,Pronoun,l>> 
S != <<type,S,*TYPE,t>> 
S != <<sem,S,*X,l>> 
S ! ~ <<DRSIn, S, *DRSIn: : *DIISInType, 1>> 
S !~ <<acceBsible,S,*h: : 
\[A ! A !~ <<*TYPE,aY,I>~\],t)>\]. 
~Vhero *TYPE will Ire our of male, female or 
rteutex llow(~vcr, it. is not su/licient to sinlply 
check the conditions in the incoming l)lLq lbr some 
tnarkvt of the right type. 
The access±b\].e relation is also dctined over the 
three(ling relations. Each utterance situation is re- 
}ah!d to ;t situation that supports the facts about 
which markers are accessible at that point m the 
discotn'se. The accessible markers for an utterance 
situati0n U are defined (inlormally) m~ follows: 
If U is a noun (or propernoun) the accessible 
markers are from that noun plus the acces- 
sil)le markers li'on, the incoming thread. 
if U is the start of a thread whose end is related 
to a determiner by tile relation body then the 
acc(,ssihl\[~ markers are those from the end of 
thai determiner's range thread. 
if U is the' start, of a rmxge thread, the accessible 
markers are those froln tlw incoming thread 
of (he relatrd determiner. 
if U is an ind('lini).(~ d('.terminer tim accessible 
nlarkers are thos(~ of the end of the body 
thread 
if ( is an every determiner I,he accessible mark 
ers are those from its incoming thread (i.e. 
does .or inclmh: Oar markers introduced in 
Lhe range and body threads). 
otherwise the accessible markers are those of the 
incoming thread 
These couditiolis can e~Lsily be represented by ASTL 
¢Ollst,rain Ls 
C~iven the abow! descriptions: a syntactic back- 
bone a I)RS represent, aLien, threading and defini- 
tion for accessibility) we can refill I)RSs for simple 
(liscourses. The coverage is that of \[6\]. This still 
allows an example of donkey anaphora ;is ill "every 
man with a do)lkey likes it" The DRS0ut for the 
discourse utterance situation is. 
AcrEs Dv.'COLING-92, NAbrrlis, 23-28 AO/n' 1992 1 1 1 9 PROC. OF C(11,1NG-92, NANTES, AUG. 23-28, 1992 
every( ~ith(NA1,DA1) donkey(DA1) 
mnn(MAl) 
like (NA1 ,PN1) 
is (PNI ,DA1 ) 
) 
Discussion 
Although translation of DRT into ASTI, is possible 
there are some important consequences. Tile se- 
mantics of an ASTL DRS, briefly described above, 
requires that it is possible to tell the properties of 
every object in the situation. As situations are par- 
tial it may not be defined for everything whether it 
is a man or not, thus it is not possible to define "all 
men." (Note, lack of information does not imply 
falsity.) This is perhaps unfair to consider this as 
a problem as m the standard definitions of DR?I' it 
is required that the model be complete (all prop- 
ertics are defined on all objects) - so it seems no 
worse to require this of the situation in which we 
are finding tile trnth conditions of a 1)RS. llowever 
we could include further definitions for the every 
relation and require that there be some resource 
situation that identifies actual objects that fall in 
its scope. This technique has been used by \[4\]. 
There is the question of compositionality. It 
could be said that the threading relations are only 
partially determined eompositionally. But this 
seems exactly what the theory states and the in- 
tuition behind it. We cannot define a I)RS for a 
noun phrase nnless we know what context tile NP 
is ill. All that can be determined is partial defini- 
tion with conditions on the context. 
An important aspect of DRT is that there is a 
left to right dependency on DRSs. This does not 
necessarily mean that parsing must be left to right, 
though normally it will be. A definition of I)RT 
should inelnde this dependency and not rely on how 
a implementation happens to order processing. Tile 
ASTL definition does include a left to right depen- 
dency, without specifying a processing order on the 
inference mechanisn\]. 
Summary 
This paper has introduced tile notion of using sit- 
uation theory a.s a basic formalism in which other 
semantic theories might be defined. A computa- 
tional situation theoretic language called ASTL is 
discussed. Sitnatlon theory is suitable as basis for a 
metatheory because a representation of situations 
allows the representation of higher order objects 
necessary for describing other semantic theories. A 
possible translation of I)I~T in ASTL is given. The 
coverage is that of \[6\]. 
This translation is interesting because first it 
shows that situation theory is not some opposing 
semantic theory but that it can be used ill dis- 
cussing other theories, tIowever perhaps it is not 
surprising that a language such as ASTL is power- 
ful enough to give this translation. A feature sys- 
tem, with sets (or some definition), cycles and con- 
straints is close to what ASTL is, but it is interesting 
that these properties can be found as the basis ill a 
current semantic theory without introducing a new 
theory. Finally a situation theoretic description of 
DRT allows extensions of DRT to use the proper- 
ties of situation theory. Situations which are use- 
ful ill describing various natural language semantic 
phenomena (e.g. naked infinitives) are now readily 
available to be included in exteusious of DRT. 
Acknowledgements: This work w~s supported by an 
SEltC studentship award number 89313458. I would 
also like to thank Robin Cooper, Inn Lewin and Graeme 
Ritchie for comments anti guidance on this work. 
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Ac-r~ DE COLING-92, NANTES, 23-28 AOt3T 1992 1 1 2 0 PROC. OF COLING-92, NAI~rEs, AUG. 23-28, 1992 
