SITUATION SEMANTICS AND MACHINE TRANSLATION. 
C.J. Rupp 
CCL, UMIST 
P.O. Box 88 
Manchester M60 1QD 
Introduction 
Situation Semantics is one of the most 
recent and controversial theories in 
formal semantics. Machine Translation 
(MT) is a highly complex application 
domain, in which research is expensive 
of both time and resources. On the 
surface, the space for interaction 
between these two fields would seem 
fairly limited, and in practice the the 
application of formal semantics in MT 
has been very limited, a notable 
exception being the Rosetta project 
(Landsbergen 1982, 1987). The abstract 
translation problem however remains 
and any application must be based on 
some formalisation of the problem. 
The purpose of this paper is 
demonstrate that the enriched 
theoretical vocabulary of Situation 
Semantics offers a more intuitive 
characterisation of the translation 
process, than was .possible using more 
traditional semanuc theories. This 
demonstration will take the form of a 
formalisation of the most commonly used 
method for MT in terms of Situation 
Semantic constructs. In this respect this 
paper follows on from a previous paper 
(Johnson, Rosner & Rupp 1988), in 
which MT was presented as a testing 
ground for semantic representation 
languages. This paper will turn the issue 
around and consider what the theory of 
Situation Semantics has to offer to an 
MT application. The abstract description 
of the MT system to be considered will 
therefore remain the same. 
The paper consists of a basic 
introduction to the machinery of 
Situation Semantics, an examination of 
the problem of translation, a formal 
description of a transfer-based MT 
system and some examples of the kind 
of lexical transfer one would expect to 
define in such a system. 
Situation Semantics: The Basics. 
Situation Semantics is an informational 
approach to formal semantics. The 
philosophical basis of this theory is laid 
out in Barwise and Perry's Situations 
and Attitudes (1983) (henceforth B&P). 
Most of the structure of the theory can 
be seen as arising out of three basic 
concepts. 
Attunement: 
... an organism must be attuned to 
similarities between situations, what 
we have called uniformities, and to 
relationships that obtain between 
these uniformities... (B&P plO) 
Constraints: 
... systematic relations of a special 
sort between different types of 
situation .... These systematic 
constraints are what allow one 
situation to contain information 
about another. Attunement to these 
constraints is what allows an agent to 
pick up information from one 
situation about another. (B&P p94) 
Partiality: 
Situation types are partial. They 
don't say everything there is to say 
about everyone or even everything 
about the individuals appearing in the 
situation type. (B&P p9) 
The other main features of the theory 
can be seen as arising out of the 
interaction of these three concepts. The 
combination of attunement with 
constraints, when applied to the problem 
of linguistic meaning, leads to the 
relation theory of meaning. This states 
that language users are attuned to a 
particular type of constraint which 
relates the situation in which an 
utterance is made with the situation it is 
about. Put more formally: a sentence 
- 308 - 
relates an utterance situation, u, and a 
described situation, s. 
u\[ ls 
The notion of efficiency arises out of 
the interaction of this relation theory of 
meaning with the notion of partiality. 
Natural language expressions only carry 
a certain amount of information and so 
only partially determine the range of 
appropriate utterance and described 
situations. They can therefore be said to 
be efficient in that they can be used for 
various purposes. The notion of 
efficiency implies a clear distinction 
between meaning and interpretation. It 
is only possible to arrive at a full 
interpretation by anchoring the utterance 
situation and, as a consequence, the 
described situation to actual situations. 
The sentence itself carries only meaning. 
This theory is sufficiently fine-grained 
to permit further distinctions within the 
utterance situation, which contains two 
differing types of information: the 
discourse situation and speaker 
connections. The discourse situation is 
that part of the utterance situation 
concerned with the external facts of the 
discourse, such as the identity of the 
speaker and hearer, the temporal and 
spatial location of the conversation and 
perhaps even information about the 
mental states of the speaker and hearer. 
The discourse situation must be 
anchored before an interpretation can be 
determined. Speaker connections are 
concerned with the linguistic attunement 
that must be shared by the speaker and 
hearer for effective communication. The 
meaning relation can therefore be 
restated in terms of a discourse 
situation, d, speaker connections, c, and 
described situation, s. 
d,c\[~\]s 
The notion of speaker connections 
assumed in this paper differs slightly 
from that used in B&P, which was 
concerned primarily with determining the 
reference of certain clearly referential 
phrases, such as proper names and 
definite descriptions. In this paper it is 
assumed that most words are in some 
sense referential although their referents 
may be complex partial objects; this 
would seem a natural extension of the 
original notion. Speaker connections are 
therefore the set of culturally specific 
constraints to which the users of a 
particular language are attuned in order 
to permit them to assign meaning to 
occurrences of its expressions. 
Before considering some more recent 
developments associated with Situation 
Semantics, it will be useful to sketch 
some of the distinctions between this 
theory and more traditional semantic 
theories, such as Montague Semantics, 
with particular reference to the 
implications that these may have for an 
MT methodology, as in Landsbergen's 
Rosetta (Landsbergen 1982, 1987). 
Partiality is the most obvious 
characteristic of Situation Semantics, 
when compared to traditional possible 
world semantics of the Montagovian 
variety. In traditional theories truth 
conditions take priority over content. 
The interpretation of a sentence is the 
set of possible worlds in which it would 
be true. Each such world is total and 
therefore fully determines the answer to 
any possible question that could be 
asked about it. Some sentences will be 
necessarily true and be assigned the set 
of all possible worlds as an 
interpretation making them 
indistinguishable from one another. 
Others, including all sentences with a 
necessary truth as a constituent part, 
form sets of logically equivalent 
sentences each receiving the same 
interpretation. This results in a situation 
where attempts to generate a sentence 
from its interpretation might result in a 
sentence with completely different 
content or the required sentence 
conjoined with a potentially infinite set 
of necessar)', truths. Hence B&P's 
argument m favour of partial 
interpretations which contain only a 
fixed amount of information. This is also 
one of the reasons why MT systems 
based on Montague Semantics have 
been predominantly concerned with 
derivation rather than representing the 
interpretation of sentences. 
The relation theory of meaning also 
represents a much greater balance 
between context and content than more 
traditional theories, where context is 
usually limited to the determination of a 
few indexical terms. Although it has not 
- 309- 
yet been adequately explored, the 
contextual side of the meaning relation 
does implicitly contain the possibility of 
representing aspects of the informational 
structure of texts, which is of essential 
importance in producing representations 
for languages such as Japanese or 
German, where informational structure 
directly affects syntax. It is not possible 
to treat such languages in any depth 
even with derivational techniques, when 
only truth conditional information can be 
recorded. 
Finally traditional semantic theories 
assume a static and total interpretation 
function, which assigns denotations to 
lexical items. This poses two distinct 
problems when considering translation. 
Firstly in the case of words with more 
than one sense it is not obvious how to 
decide which denotation to choose. 
What is required is a more dynamic 
mechanism which permits the preferred 
reading to vary according to the context. 
Secondly there is the implicit 
assumption that the range of possible 
denotations is common to both 
languages concerned, and if we reject 
this assumption we are faced with the 
metaphysical problem of constructing 
appropriate denotations for each 
language out of an unknown set of 
primitives, with no philosophical 
explanation for why this problem arises. 
Schematic Representations. 
One problem with the original version 
of Situation Semantics is that it does not 
have that much to say about the 
mapping from natural language to 
Situation Semantic interpretation. The 
fragments given by B&P are essentially 
hand coded and give no indication as to 
how Situation Semantics might be 
incorporated into a larger more 
syntactically oriented grammar. More 
recent work by Fenstad, Halvorsen, 
Langholm and van Benthem (1987) 
demonstrates a method of incorporating 
Situation Semantics into LFG 
grammars, and HPSG (Pollard & Sag 
1987) adopts a similar approach. The 
combination of unification-based 
grammar formalisms with Situation 
Semantics is a very natural move given 
the role played by partiality in both 
theories. (See for example Barwise's 
comment (Barwise & Perry 1985, p143). 
Unification-based approaches to 
Situation Semantics generally require 
the inclusion of a level of abstract 
representation which only partially 
determines the range of possible 
interpretations. This can be seen as the 
meaning carried by the sentence under a 
range of interpretations, but it will be 
less ambiguous that the original 
sentence as different syntactic analyses 
will give rise to different representations. 
It is possible to state the meaning 
relation imposed by such a 
representation or situation schema in 
the same terms as were used for the 
sentence. 
d,c\[sit.~\]s 
The relation between a sentence, 
and its representation sit.qb will be given 
by a grammar G, which maps strings of a 
language L to members of a class of 
representations R, (which will be in the 
form of Directed Acyclic Graphs). In 
order to reflect the semantic relation 
between these two objects it will be 
necessary to define two auxiliary 
"interpretation functions" which 
determine the set of possible 
interpretations so that 
InL(¢) = { <d,c,s> I d,c\[¢\]s } 
InR(sit.q) = { <d,c,s> I d,c\[sit.dd\]s } 
The grammar then defines the relation 
G = { <0,sit.C> I¢ e L, 
sit.¢ ~ R, 
InR(sit.¢) c_ InL(¢) } 
It could be argued that the introduction 
of an extra level of representation could 
pose some problems for the foundations 
of the theory in that it inevitably attracts 
comparisons with Discourse 
Representation Theory (DRT) and 
representational theories of semantics 
which assign psychological significance 
to their intermediate levels of 
representation. The key to 
understanding the nature of situation 
schemata is to see them as containing 
just the information which may be 
carried by the use of the construct they 
represent. Their significance lies 
- 310- 
therefore not in the minds of the 
language users but in the communicative 
interaction between them. This makes 
this level of representation the perfect 
medium for the study of translational 
equivalences. 
Translation Equivalence within 
a Situational Framework. 
This section is concerned with the two 
essential problems of any approach to 
MT: the nature and extent of the 
information that must be preserved, and 
the nature of the alteration which must 
be effected. Following on from the 
previous section it would seem that a 
partial representation which carried the 
content of the text ought to supply 
sufficient information to be preserved. 
This would represent the meaning of the 
text while leaving ambiguities of 
interpretation underspecified. This would 
effectively freeze the described 
situation, leaving the context side of the 
meaning relation as the only domain for 
translation operations. 
A text places fewer constraints on its 
context than a conversation, because the 
author and reader know a lot less about 
each other than do the corresponding 
speaker and hearer. It follows from this 
that much of what a text does have to 
say about its context will remain 
constant under translation. If an author 
assumes his reader to have specialised 
knowledge of a particular subject domain 
then this requirement should not be 
affected by translation. This type of 
information is external to the text and 
therefore would not appear in the 
representation of the content and so 
would not be affected by translation. The 
only major alteration required in the 
context of the text is that the reader and 
author are considered to be users of the 
target language rather than the source 
language. This will not greatly affect the 
external facts of the interaction so the 
discourse situation can remain constant. 
It will however drastically affect the 
linguistic attunements that the author 
and reader must share in order to 
communicate. These are culturally 
conditioned and affect not only the way 
that words may be used to refer to the 
uniformities that make up the content of 
the text, but also the range of 
uniformities that it is possible to refer to. 
This association of linguistic forms with 
uniformities in the real world is provided 
by speaker connections and these will 
be the domain over which translation 
must operate. Speaker connections do 
however cover certain text internal 
forms of reference, such as anaphoric 
binding; these should also remain 
predominantly impervious to translation. 
It is mainly those connections involved 
in reference into the described situation 
that must be altered. While this domain 
only represents a very small part of the 
situational formalisation of the meaning 
relation it still represents a vast area of 
potential variation. 
Transfer-based MT. 
The problem space for MT is 
traditionally viewed as being triangular 
in shape (Vauquois 1979). In this model 
the problem of translating between texts 
is reduced to that of a transfer mapping 
between abstract representation of 
those texts. It is usually assumed that 
there is a direct relationship between 
the complexity of the transfer operations 
and the level of abstraction of the 
representations; some of the issues 
involved in this trade-off are discussed 
in Krauwer & des Tombe (1984). The 
limit case is where the representations 
are sufficiently abstract that transfer 
becomes vacuous: this is exemplified by 
the interlingual approach adopted in 
Rosetta (Landsbergen 1982). Increased 
abstraction can however lead to the loss 
of relevant information and implies 
recourse to a culturally independent set 
of primitives. The adoption of a 
situational framework for an MT system 
places interesting constraints on the 
method to be employed, because both 
the abstract representational level and 
the nature of the transfer mapping are 
determined by the theoretical 
framework. Interestingly, this turns out 
to be the kind of transfer-based method 
most commonly advocated within 
syntactically oriented approaches to MT. 
Within the current model, with 
situation schemata functioning as the 
representational level in a transfer- 
based MT system, the abstraction from 
text to representation would be that 
~,.-v - 311 - 
defined by the grammar relation, G, 
above, except that two versions of this 
relation are now required. The parsing 
relation would be given by a source 
language grammar, GsougcE. 
Gsot~c~ = { <~,sit.~> I~ ~ Ls, 
sit.~ E Rs, 
InRs(sit.~) c_ InLs(~) } 
Generation would, similarly, use a 
target language grammar, GTARG~T 
GTARGET = { <~',sit.¢~'> I ~' ~ Lt, 
sit.~' ~ Rt, 
InRt(sit.¢~') ~ InLt(¢~') } 
The transfer relation can then be 
defined as a translation relation across 
representations, TR, expressed in terms 
of: the two representations, sit.~ and 
sit.¢~', a constant described situation, s, 
and for the purposes of this model a 
constant discourse situation, d. The 
actual mapping, K, will be defined across 
the two sets of speaker connections, c 
and c'. 
TR = { <sit.~,sit.~'> I d,c\[sit.~\]s 
d,c'\[sit.¢'\]s 
K(c,c') } 
The translation relation across 
languages, TL, can then be expressed in 
terms of the definitions given above. 
TL = { <~,~'> I <~,sit.~> ~ GsotrRC E 
<¢~',sit.¢~'> ~ GTARC~T 
<sit.@,sit.¢> ~ TR } 
In the same way that MT by transfer 
reduces the translation problem to a 
translation across representations, so 
this particular formalisation of the 
method condenses all the translation 
operations onto a single K-mapping 
across speaker connections. This 
process of restricting the domain over 
which translation relations hold also 
reduces their scope. The discussion of 
translation equivalence was framed in 
terms of texts, the formalisation of the 
translation method is expressed in 
terms of sentence, but speaker 
connections are a set of constraints on 
the use of individual words. It might 
appear that the restrictions of the 
transfer mapping to a lexical level 
smacks of regression towards primitive 
word-for-word translation, but with the 
assistance of recent developments 
within unification-based grammar 
formalisms nothing could be further from 
the truth. There are two features shared 
by UCG (Zeevat et al. 1987), HPSG 
(Pollard & Sag 1987) and recent 
versions of LFG (Fenstad et al. 1987, 
Halvorsen 1987) which make the 
implementation of such lexical transfer 
possible. The fin'st is the combination of 
syntactic, semantic and even 
phonological information expressed in 
the same form at all levels of the 
grammar. This allows for the incremental 
evaluation of constraints across these 
various domains. The second is the 
concentration of information in the 
lexicon, including information concerning 
the combinatory behaviour of individual 
lexical items. These two principles, 
known as constraint propagation and 
lexicalism, should make it possible to 
define lexical transfer relations in terms 
of the representations associated with 
individual words of the language, 
without compromising the ability to 
specify a wider context. 
Lexical Transfer based on 
Speaker Connections. 
Having outlined an approach to 
translation based on transfer relations 
over the representations associated 
with individual lexical items, it is 
necessary to consider how such an 
approach might be implemented. This 
involves two basic issues: the formal 
nature of such relations and the 
information that they must express. This 
discussion will be based on an MT 
prototype under development at ISSCO 
Geneva (Johnson et al. 1988) which 
employs a grammar development tool for 
unification grammars known as UD, or 
Unification Device (Johnson & Rosner 
1989). Within this environment a 
representational format has been 
developed based on the situation 
schemata of (Fenstad et al. 1987). This 
will be the framework in which the issue 
of lexical transfer over graph-structured 
representations will be considered. 
One obvious point of reference in 
- 312 - 
considering relations between attribute- 
value graphs is the kind of lexical rule 
found in PATR type environments 
(Shieber 1984, Karttunen 1986). These 
are essentially relations between graphs 
and are used to treat such phenomena 
as passivisation. A similar mechanism 
could be used to implement lexical 
transfer relations. There would however 
be one major change in the formulation of 
such rules, namely the fact that the 
representations to be related belong to 
different grammars and so are 
associated with different syntactic 
structures. This would affect the way 
that the root of the graph was 
associated with the lexical item and the 
way that information about the 
surrounding context was passed on. In a 
lexical rule information to be preserved 
can simply be equated, but here a 
translational equivalence is required. 
There are a number of ways in which 
this correspondence between elements 
of different domains might be treated. 
These include the kind of structural correspondence 
used for relating syntax 
and semantics in recent work on LFG 
(Halvorsen 1987, Kaplan & Halvorsen 
1988, Kaplan, Netter, Wedekind & 
Zaenen 1989) and also bilingual lexical 
entries as in Beaven & Whitelock 
(1988). The UD formalisation given here 
will assume a slightly more flexible 
version of the latter approach, in that not 
only is the requirement to associate 
entries of different lexicons recognised, 
but also the need to be free of the 
immediate syntactic structure. 
Before commenting on a UD 
implementation of such lexical relations 
it is necessary to point out that the UD 
environment does not support lexical 
rules of the form mentioned above. There 
is instead a more generalised notion of 
relational abstraction over the 
representational domain. This permits 
the relational characterisation of most of 
the phenomena usually treated by lexical 
rules, but not the interpretation under 
which such rules carry out non- 
monotonic operations on existing 
structures. Relational abstractions also 
permit lexical relations to be broken 
down into more specific generalisations 
allowing for a more modular treatment of 
such phenomena. 
Some examples may demonstrate how 
this technique might be applied to some 
of the less trivial equivalences between 
representations. The often quoted 
equivalence between the Dutch sentence 
Ik zwem graag. I swim willingly. 
with the representation 
and the English 
I like to swim. 
involves a difference in the syntactic 
category used to express essentially the 
same uniformity. This would be reflected 
in the structure of the semantic 
representations assigned to these 
sentences. 
Ind ~ype sit-'\] 
Cond el I-  FTY e re-q" 
_coo./  
Rel c(graag) 
(D 
c(zwemmen)U 
Pol 1 
Fig. 1 - A Situation Schema for the 
Dutch sentence: Ik zwem graag. 
The Dutch representation (Fig.l) shows graag 
as a relation over pairs of 
relational objects where the English 
(Fig.2) represents like as a relation 
between an entity and a situation. 
- 313 - 
s,t--1 
Cond Rel c(like) 
Arg 1 c(/) 
_ t on' I 
Pol 1 
-- Rel c(swim) 
Arg 1"~ c(/)--'\] 
Pol 1 
Fig.2 - A Situation Schema for the 
English sentence: I like to swim. 
m 
The relation between the semantic 
representations of the two words can be 
expressed by the abstraction LTR 
(Lexical Transfer) as follows: 
LTR(Dutch,English) 
<Dutch ind type> = 
<English ind type> = sit 
<Dutch cond> --- \[DC\] 
<English cond> - \[EC\] 
<EC rel> = like(_.) 
!TR(<DC arg I>,<EC arg 1>) 
<EC arg 2 ind type> = sit 
<EC arg 2 cond> = \[ESC\] 
<DC rel ind type> = rel 
<DC rel cond> -- \[DRC\] 
<DRC rel> = graagfEnglish) 
<DRC arg 1> = <DC rel ind val> 
!TR(<DRC arg 2>,<ESC rel>) 
<ESC arg 1> = <EC arg 1> 
In practice this definition would not 
require quite so much code as it would 
be more efficient to draw on abstractions 
generalising across large numbers of 
translation relations. The only other 
abstraction referred to here, TR, is the 
necessary reference to translational 
rather than equational equivalence 
where reference is made to the wider 
context of the two representations. This 
definition is framed solely in terms of the 
semantic representations and the direct 
connection between the two 
representations is made by embedding 
one under the lexical leaf of the other. 
This method of representing the 
correspondence between actual lexical 
entries is highly experimental and has 
not yet been applied to any of the larger 
grammars developed within the UD 
formalism. It does however avoid one of 
the more basic problems with the UD 
implementation of situation schemata: 
the fact that while it is relatively easy to 
assert the existence of a piece of 
representation, it is not possible to 
ensure that this representation be 
associated with an actual piece of 
syntactic structure. It is relatively easy 
to emulate projection mechanisms such 
as the a and @ mappings of Halvorsen 
& Kaplan (1988) by the use of attributes 
within a larger representation, but it is 
not currently possible to reproduce the 
corresponding inverse mappings. 
The relation defined above could be 
described using conventional LFG 
notations and projections, including a 't 
mapping for translation between 
semantic representations. This would 
however require a slight alteration in the 
representation language to permit only 
one condition on each object. The 
resulting definition would consist of the 
following set of equations, in which * is 
the c-structure node associated with the 
word graag, a a projection from c- 
structure to semantic representation and 
x the transfer projection from source 
representation to target representation. 
fin Kaplan et al. (1989) translation 
relations are predominantly defined in 
terms of a projection x across f- 
structures and the semantic projection is 
referred to as 'g.) 
- 314 - 
(o* ind type) =(1;o * ind type) 
(o* ind type) = sit 
(o* cond tel ind type) = rel 
(o* cond tel cond rel) = graag 
('¢o* cond rel) = like 
x(o* arg 1) = (zo* arg 1) 
'¢(o* cond rel cond arg 2) = 
(xo * cond arg 2 cond rel) 
(xo* cond arg 2 ind type) = sit 
(o* cond rel ind type) = rel 
(o* cond rel cond arg 1) = 
(o* cond rel ind val) 
(xo* cond arg 2 cond arg 1) = 
(xo* cond arg 1) 
This also expresses the translational 
equivalence of the two words purely in 
terms of their semantic representations, 
but this formalism does in principle 
permit the definition of inverse 
projections so that o'lxo* would be 
the c-structure node associated with the 
word like. In order to take advantage of 
this device it is however necessary to 
sacrifice the increased expressive power 
of a representation language defined in 
UD and the highly modular treatment 
that the use of relational abstractions 
provides. While both of these 
formalisms permit the specification of 
the required lexical transfer relations 
without the need to route all information 
through the source language syntax, it 
would seem more appropriate to explore 
the range of appropriate transfer 
relations within the UD formalism. 
A more complex example of this kind of 
lexical transfer relation might be taken 
from comparing the use of verbs of 
motion in English and French. In French 
the verb often describes uniformities 
associated with motion and its direction 
and any specification of manner might 
have to rely on an adverbial modifier as 
in 
I1 descend la rue en courant. 
He go-down the road runningly 
The representation associated with 
this sentence is given in Fig.3. 
I ,,e 
o.d Re,  Indp,,e re \]l /  "clJ/ 
L~ ond ~J 
m Rel 
Arg 
Pol 
Arg 
e(courir) 
E e(descendre~_ 
1_ ue) \] Rei c(r 
1 
m 
m 1 c(i/) 
2 "-~drType e ~- 
_.Cond I I l_. / 
Pol 1 
Fig.3 - A Situation Schema for the 
French sentence: 
I1 descend la rue en courant. 
In English however verbs are usually 
more concerned with the manner of the 
motion and the direction is left to a 
prepositional phrase, as in the 
corresponding 
He runs down the road. 
which receives the representation in 
Fig.4. 
- 315 - 
~nd ~ype sit-\] 
Cond Rel c(run) 
Arg 1 c(he) 
2 ~nd mType !o~ 
Cond 
eol I / 
/ 
2 
m 
Pol 1 
--~d mType e~ 1 
ba'C J 
._Cond E Rel--Of " 
Ar r7 (2fj 
Pol 1 
Fig.4 - A Situation Schema for the 
English sentence: 
He ran down the road. 
The following abstraction defines a 
relation between the English verb run 
and the French verb courir. 
LTR(English,French) 
<English ind type> = 
<French ind type> = sit 
<English cond> = \[EC\] 
<French cond> = \[FC\] 
<EC rel> = run(French) 
<FC rel> = courir(_) 
!Trans(<EC arg I>,<FC arg I>) 
LTR(English,French) 
<English ind type> = 
<French ind type> = sit 
<English cond> = \[EC\] 
<French cond> = \[FC\] 
<EC rel> = run(French) 
<FC rel cond> = \[FCR\] 
<FCR rel> = courir(_) 
lTrans(<EC arg I>,<FC arg 1>) 
!Trans(<EC arg 2>,T) 
<EC arg 2 ind type> = loc 
There two are clauses, denoting two 
possible transfer relations. The first 
treats the simple case where there is no 
directional prepositional phrase in the 
English and the correspondence is very 
simple as both verbs refer to a relation 
over one entity argument. The second 
clause however treats the case where 
the second argument to the English verb 
is locational, as in the example above, 
which causes the corresponding French 
expression to be construed as a relation 
over relational objects, and therefore an 
adverbial modifier. The formation of such 
a modifier must be left to the French 
syntax and the main verb must be 
supplied by the translation of the 
prepositional phrase. This definition 
makes a lot of assumptions about the 
kind of transfer relations that will be 
defined on other words. It also implies 
that a word like the French en that 
makes no contribution to the semantic 
representation, as it only converts a 
verb form into an adverbial phrase, 
should be capable of performing major 
changes to the translational behaviour of 
the verb it applies to. 
In the previous example the 
distribution of information across the 
uniformities that the two languages 
were able to refer to was clearly 
different and this was treated by a 
complex structural relation over the 
representations assigned to the words 
involved. With a relatively simple case 
like this it might seem more appropriate 
to appeal to some deeper level of 
semantic primitives to resolve such 
differences, but the task of lexical 
decomposition over multilingual 
vocabularies is obviously doomed by the 
fact that for most domains there is no 
obvious constraint on where a culture 
will decide to draw a distinction. This 
holds for most domains covered by open 
- 316 - 
class words that provide most of the 
content of a text. There are however a 
few domains that are so structured that 
they are amenable to decomposition. 
When languages refer to uniformities in 
these domains it is usually with 
constructs that are systematically 
incorporated into their morphology or 
with words from distinctly closed 
classes. These domains correspond to 
areas that have often caused major 
problems for MT, such as tense, aspect, 
modality and determination. In some of 
these domains it has already become 
accepted to appeal to an abstract 
representation that is essentially 
language independent, as in the work of 
van Eynde on tense and aspect (e.g. 
1988). It is interesting that the 
primitives required for such 
representations correspond to the kind 
of structural relations required in the 
different object domains of Situation 
Semantics: locations, relations, 
situations and entities. It is not possible 
to present any interesting examples of 
the treatment of such phenomena here 
as there is still much work to be done on 
determining appropriate sets of primitive 
structural relations, though Cooper 
(1985,1986) presents a basis for the 
treatment of tense and aspect within 
Situation Semantics. 
Conclusion. 
This paper has presented a formal 
description of an approach to MT that is 
based on principles drawn from Situation 
Semantics, but which utilises the same 
basic architecture as more syntactically 
motivated systems. It has also 
presented some examples of how such 
an approach might be implemented 
within current unification grammar 
formalisms. While this approach has yet 
to be implemented on any major scale, 
related work at ISSCO, Geneva has 
produced grammars for moderately large 
fragments of German and French which 
deliver the kind of representation 
required by such a system. 
Acknowledgements. 
This research was supported by an 
SERC studentship (No. 8632138X). 
I would also like to express my 
gratitude to Rod Johnson for providing 
both intellectual and technical support 
for this research. 
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