TRANSLATION BY STRUCTURAL CORRESPONDENCES 
Ronald M. Kaplan* 
Klaus Netter** 
J iirgen Wedekind* * 
Annie Zaenen* 
*Xerox Palo Alto Research Center, 
3333 Coyote Hill Road 
Palo Alto, CA 94304, USA 
Kaplan.pa@xerox.com 
** Institut fiir Maschinelle Sprachverarbeitung, 
17 Keplerstrafle 
D-7000 Stuttgart 1, FRG 
Bualis@rus.uni-stuttgart.dbp.de 
ABSTRACT 
We sketch and illustrate an approach to 
machine translation that exploits the potential 
of simultaneous correspondences between 
separate levels of linguistic representation, as 
formalized in the LFG notion of codescriptions. 
The approach is illustrated with examples 
from English, German and French where the 
source and the target language sentence show 
noteworthy differences in linguistic analysis. 
INTRODUCTION 
In this paper we sketch an approach to 
machine translation that offers several 
advantages compared to many of the other 
strategies currently being pursued. We define 
the relationship between the linguistic 
structures of the source and target languages 
in terms of a set of correspondence functions 
instead of providing derivational or procedural 
techniques for converting source into target. 
This approach permits the mapping between 
source and target to depend on information 
from various levels of linguistic abstraction 
while still preserving the modularity of 
linguistic components and of source and target 
grammars and lexicons. Our conceptual 
framework depends on notions of structure, 
structural description, and structural 
correspondence. In the following sections we 
outline these basic notions and show how they 
can be used to deal with certain interesting 
translation problems in a simple and 
straightforward way. In its emphasis on 
description-based techniques, our approach 
shares some fundamental features with the 
one proposed by Kay (1984), but we use an 
explicit projection mechanism to separate out 
and organize the intra- and inter-language 
components. 
Most existing translation systems are either 
transfer-based or interlingua-based. 
Transfer-based systems usually specify a 
single level of representation or abstraction at 
which transfer is supposed to take place. A 
source string is analyzed into a structure at 
that level of representation, a transfer 
program then converts this into a target 
structure at the same level, and the target 
string is then generated from this structure. 
Interlingua-based systems on the other hand 
require that a source string has to be analyzed 
into a structure that is identical to a structure 
from which a target string has to be generated. 
Without further constraints, each of these 
approaches could in principle be successful, An 
interlingual representation could be devised, 
for example, to contain whatever information 
is needed to make all the appropriate 
distinctions for all the sentences in all the 
languages under consideration. Similarly, a 
transfer structure could be arbitrarily 
configured to allow for the contrastive analysis 
of any two particular languages. It seems 
unlikely that systems based on such an 
undisciplined arrangement of information will 
ever succeed in practice. Indeed, most 
translation researchers have based their 
systems on representations that have some 
more general and independent motivation. 
The levels of traditional linguistic analysis 
{phonology, morphology, syntax, semantics, 
discourse, etc.) are attractive because they 
provide structures with well-defined and 
coherent properties, but a single one of these 
- 272 - 
levels does not contain all the information 
needed for adequate translation. The 
D-structure level of Government-Binding 
theory, for example, contains information 
about the predicate-argument relations of a 
clause but says nothing about the surface 
constituent order that is necessary to 
accurately distinguish between old and new 
information or topic and comment. As another 
example, the functional structures of 
Lexical-Functional Grammar do not contain 
the ordering information necessary to 
determine the scope of quantifiers or other 
operators. 
Our proposal, as it is set forth below, allows 
us to state simultaneous correspondences 
between several levels of source-target 
representations, and thus is neither 
interlingual nor transfer-based. We can 
achieve modularity of linguistic specifications, 
by not requiring conceptually different kinds of 
linguistic information to be combined into a 
single structure. Yet that diverse information 
is still accessible to determine the set of target 
strings that adequately translate a source 
string. We also achieve modularity of a more 
basic sort: our correspondence mechanism 
permits contrastive transfer rules that depend 
on but do not duplicate the specifications of 
independently motivated grammars of the 
source and target languages (Isabelle and 
Macklovitch, 1986; Netter and Wedekind, 
1986). 
A GENERAL ARCHITECTURE FOR 
LINGUISTIC DESCRIPTIONS 
Our approach uses the equality- and 
description-based mechanisms of 
Lexical-Functional Grammar. As introduced 
by Kaplan and Bresnan (1982), 
lexical-functional grammar assigns to every 
sentence two levels of syntactic representation, 
a constituent structure (c-structure) and a 
functional structure (f-structure). These 
structures are of different formal types--the 
c-structure is a phrase-structure tree while the 
f-structure is a hierarchical finite 
function--and they characterize different 
aspects of the information carried by the 
sentence. The c-structure represents the 
ordered arrangement of words and phrases in 
the sentence while the f-structure explicitly 
marks its grammatical functions (subject, 
object, etc.). For each type of structure there is 
a special notation or description-language in 
which the properties of desirable instances of 
that type can be specified. Constituent 
structures are described by standard 
context-free rule notation (augmented with a 
variety of abbreviatory devices that do not 
change its generative power), while 
f-structures are described by Boolean 
combinations of function-argument equalities 
stated over variables that denote the 
structures of interest. Kaplan and Bresnan 
assumed a correspondence function mapping 
between the nodes in the c-structure of a 
sentence and the units of its f-structure, and 
used that piecewise function to produce a 
description of the f-structure (in its equational 
language) by virtue of the mother-daughter, 
order, and category relations of the c-structure. 
The formal picture developed by Kaplan and 
Bresnan, as clarified in Kaplan (1987), is 
illustrated in the following structures for 
sentence (1): 
(I) (a) The baby fell. 
(b) ¢ 
rtl r 
~I~ ~'~RED ' fall<\[baby\],' 7 
/ ~\ \ ITENSE past / 
\ ~\[ \[ \[NUMB sg II 
/ I /2~ PEC RED th 
The c-structure appears on the left, the 
f-structure on the right. The c-structure- 
to-f-structure correspondence, ~b, is shown by 
the linking lines. The correspondence ¢ is a 
many-to-one function taking the S, VP and V 
nodes all into the same outermost unit of the 
f-stucture, fl. 
The node-configuration at the top of the tree 
satisfies the statement S~NP VP in the 
context-free description language for the 
c-structure. As suggested by Kaplan (1987}, 
this is a simple way of defining a collection of 
more specific properties of the tree, such as the 
fact that the S node (labeled nl) is the mother 
of the NP node (n2). These facts could also be 
written in equational form as M(n2)=nl, 
- 273 - 
where M denotes the function that takes a 
tree-node into its mother. Similarly, the 
outermost f-structure satisfies the assertions 
(/'1 TENSE) = past, (fl SUBJ) = f2, and 
(f2 NUMB)=Sg in the f-structure description 
language. Given the illustrated 
correspondence, we also know that fl=d~(nl) 
and f2--~b(n2). Taking all these propositions 
together, we can infer first that 
(dl)(n 1) SUBJ) = (l)(n2) and then that 
(dl)(M(n2)) SUB,/) = ~b(n2). This equation 
identifies the subject in the f-structure in 
terms of the mother-daughter relation in the 
tree. 
In LFG the f-structure assigned to a sentence 
is the smallest one that satisfies the 
conjunction of equations in its functional 
description. The functional description is 
determined from the trees that the c-structure 
grammar provides for the string by a simple 
matching process. A given tree is analyzed 
with respect to the c-structure rules to identify 
particular nodes of interest. Equations about 
the f-structure corresponding to those nodes 
(via ~b) are then derived by substituting those 
nodes into equation-patterns or schemata. 
Thus, still following Kaplan (1987), if * 
appears in a schema to stand for the node 
matching a given rule-category, the functional 
description will include an equation containing 
that node (or an expression such as n2 that 
designates it) instead of *. The equation 
(~(M(n2)) SUBJ)----~b(n2) that we inferred above 
also results from instantiating the schema 
(di)(M(*)) SUBJ)=¢(*) annotated to the NP 
element of the S rule in (2a) when that 
rule-element is matched against the tree in 
(lb). Kaplan observes that the ? and 
metavariables in the Kaplan/Bresnan 
formulation of LFG are simply convenient 
abbreviations for the complex expressions 
~b(M(*)) and ~(*), respectively, thus explicating 
the traditional, more palatable formulation in 
(2b). 
(2) (a) S--* NP VP 
¢(M(*)) SUBJ) = dl)(*) dl)(M(*)) = ~b(*) 
(b) S -4 NP VP 
(1' SUBJ)= t = 
This basic conception of descriptions and 
correspondences has been extended in several 
ways. First, this framework has been 
generalized to additional kinds of structures 
that represent other subsystems of linguistic 
information (Kaplan, 1987; Halvorsen, 1988). 
These structures can be related by new 
correspondences that permit appropriate 
descriptions of more abstract structures to be 
produced. Halvorsen and Kaplan (1988), for 
example, discuss a level of semantic structure 
that encodes predicate-argument relations and 
quantifier scope, information that does not 
enter into the kinds of syntactic 
generalizations that the f-structure supports. 
They point out how the semantic structure can 
be set in correspondence with both c-structure 
and f-structure units by means of related 
mappings o and o'. Kaplan (1987) raises the 
possibility of further distinct structures and 
correspondences to represent anaphoric 
dependencies, discourse properties of 
sentences, and other projections of the same 
string. 
Second, Kaplan (1988) and Halvorsen and 
Kaplan (1988) discuss other methods for 
deriving the descriptions necessary to 
determine these abstract structures. The 
arrangement outlined above, in which the 
description of one kind of structure (the 
f-structure) is derived by analyzing or 
matching against another one, is an example of 
what is called description-by-analysis. The 
semantic interpretation mechanisms proposed 
by Halvorsen (1983) and Reyle (1988) are other 
examples of this descriptive technique. In this 
method the grammar provides general 
patterns to compare against a given structure 
and these are then instantiated if the analysis 
is satisfactory. One consequence of this 
approach is that the structure in the range of 
the correspondence, the one whose description 
is being developed, can only have properties 
that are derived from information explicitly 
identified in the domain structure. 
Another description mechanism is possible 
when three or more structures are related 
through correspondences. Suppose the 
c-structure and f-structure are related by ¢ as 
in (2a) and that the function o then maps the 
f-structure units into corresponding units of 
semantic structure of the sort suggested by 
Fenstad et al. (1987). The formal arrangement 
is shown in Figure 1 (next page). This 
configuration of cascaded correspondences 
opens up a new descriptive possibility. If o and 
~b are both structural correspondences, then so 
is their composition o o ~b. Thus, even though 
the units of the semantic structure correspond 
directly only to the units of the f-structure and 
have no immediate connection to the nodes of 
- 274- 
S 
NP VP 
I I ! The baby f II 
@ 
I RED ' fall<\[baby\]>' ENSE past 'baby' /z~PEC r~EF ÷ " LPRED the ftL 
Figure 1 
o 
ol 
T~EL fall I 
,° "%1 PEC ~ET THE~ 
ARG1 ~EL bab~' r'J 
I ARG1 ~ II o2LC OND 
LPOL 1 JJ 
i No 0o i.D-toc-J  \]~EL PRECED~ LOC OND IARG1 / LARG2 LOC-D 
POL 1 
the c-structure, a semantic description can be 
formulated in terms of c-structure relations. 
The expression o(d~(M(*))) can appear on a 
c-structure rule-element to designate the 
semantic-structure unit corresponding to the 
f-structure that corresponds to the mother of 
the node that matches that rule-element. 
Since projections are monadic functions, we 
can remove the uninformative parentheses and 
write (oqbM* ARG1)"-o(dpM* SUBJ), or, using the 
metavariable, (o ~ ARGI) ---- o( I" SUBJ). 
Schemata such as this can be freely mixed with 
LFG's standard functional specifications in 
lexical entries and c-structure rules. For 
example, the lexical entry for fall might be 
given as follows: 
(3) fall V ( ~' PRED) --'fall' 
lol REL) = fall 
ARGI) -- O( ~ SUBJ) 
Descriptions formulated by composing 
separate correspondences have a surprising 
characteristic: they allow the final range 
structure (e.g. the semantic structure) to have 
properties that cannot be inferred from any 
information present in the intermediate (f-) 
structure. But those properties can obtain only 
if the intermediate structure is derived from an 
initial (c-) structure with certain features. For 
example, Kaplan and Maxwell (1988a) exploit 
this capability to describe semantic structures 
for coordinate constructions which necessarily 
contain the logical conjunction appropriate to 
the string even though there is no reasonable 
place for that conjunction to be marked in the 
f-structure. In sum, this method of description, 
which has been called codescription, permits 
information from a variety of different levels to 
constrain a particular structure, even though 
there are no direct correspondences linking 
them together. It provides for modularity of 
basic relationships while allowing certain 
necessary restrictions to have their influence. 
The descriptive architecture of LFG as 
extended by Kaplan and Halvorsen provides 
for multiple levels of structure to be related by 
separate correspondences, and these 
correspondences allow descriptions of the 
various structures to be constructed, either by 
analysis or composition, from the properties of 
other structures. Earlier researchers have 
applied these mechanisms to the linguistic 
structures for sentences in a single language. 
In this paper, we extend this system one step 
further: we introduce correspondences 
between structures for sentences in different 
languages that stand in a translation relation 
to one another. The description of the target 
language structures are derived via analysis 
and codescription from the source language 
structures, by virtue of additional annotations 
in c-structure rules and lexical entries. Those 
descriptions are solved to find satisfying 
solutions, and these solutions are then the 
input to the target generation process. 
In the two language arrangement sketched 
below, we introduce the ~ correspondence to 
map between the f-structure units of the source 
language and the f-structure units of the target 
language. The o correspondence maps from the 
f-structure of each language to its own 
corresponding semantic structure, and a 
second transfer correspondence z' relates those 
structures. 
- 275 - 
(4) 
Source ," ", Target 
s • 
O----------~O semantic structure o/ 
O ~-- .~ >O f-structure 
d~/ ~ ~:-structure O O 
This arrangement allows us to describe the 
target f-structure by composing dp and ~ to form 
expressions such as z(dpM* COMP)= (~bM* 
XCOMP) or simply ~( ~ COMP)-- (~ ~ XCOMP)). 
This maps a COMP in the source f-structure into 
an XCOMP in the target f-structure. The 
relations asserted by this equation are depicted 
in the following source-target diagram: 
(5) 
Source Target 
,Io:: 
As another example, the equation 
Z'(O~ ARG1)=(O'~ ARG1) identifies the first 
arguments in the source and target semantic 
structures. The equation ~'o( I' SUBJ)-- 
o(z t TOPIC) imposes the constraint that the 
semantics of the source SUBJ will translate via 
~' into the semantics of the target TOPIC but 
gives no further information about what those 
semantic structures actually contain. 
Our general correspondence architecture 
thus applies naturally to the problem of 
translation. But there are constraints on 
correspondences specific to translation that 
this general architecture does not address. For 
instance, the description of the 
target-language structures derived from the 
source-language is incomplete. The target 
structures may and usually will have 
grammatical and semantic features that are 
not determined by the source. It makes little 
sense, for example, to include information 
about grammatical gender in the transfer 
process if this feature is exhaustively 
determined by the grammar of the target 
language. We can formalize the relation 
between the information contained in the 
transfer component and an adequate 
translation of the source sentence into a target 
sentence as follows: for a target sentence to be 
an adequate translation of a given source 
sentence, it must be the case that a minimal 
structure assigned to that sentence by the 
target grammar is subsumed by a minimal 
solution to the transfer description. One 
desirable consequence of this formalization is 
that it permits two distinct target strings for a 
source string whose meaning in the absence of 
other information is vague but not ambiguous. 
Thus this conceptual and notational 
framework provides a powerful and flexible 
system for imposing constraints on the form of 
a target sentence by relating them to 
information that appears at different levels of 
source-language abstraction. This apparatus 
allows us to avoid many of the problems 
encountered by more derivational, 
transformational or procedural models of 
transfer. We will illustrate our proposal with 
examples that have posed challenges for some 
other approaches. 
EXAMPLES 
Changes in grammatical function. Some quite 
trivial changes in structure occur when the 
source and the target predicate differ in the 
grammatical functions that they subcategorize 
for. We will illustrate this with an example in 
which a German transitive verb is translated 
with an intransitive verb taking an oblique 
complement in French: 
(6) (a) Der Student beantwortet die Frage. 
(b) L'6tudiant r6pond it la question. 
We treat the oblique preposition as a PRED that 
itself takes an object. Ignoring information 
about tense, the lexical entry for beantworten 
in the German lexicon looks as follows: 
(7) beantworten V ( T PRED)="oeantworten<( t SUBJ)( t OBJ)>' 
while the transfer lexicon for beantworten 
contains the following mapping specifications: 
- 276- 
(¢ I PRED FN) = r6pondre (8) (~ SUBJ)=~(TSUBJ) 
(~ { AOBJ OBJ) ---- ~( '1' OBJ) 
We use the special attribute FN to designate the 
function-name in semantic forms such as 
%eantworten < ( T SUBJ)( T OBJ) >'. In this 
transfer equation it identifies r~pondre as the 
corresponding French predicate. This 
specification controls lexical selection in the 
target, for example, selecting the following 
French lexical entry to be used in the 
translation: 
(9) rdpondre V ( 1' PRED)='r6pondre<( 1` SUBJ)( 1` AOBJ)>' 
With these entries and the appropriate but 
trivial entries for der Student and die Frage we 
get the following f-structure in the source 
language and associated f-structure in the 
target language for the sentence in (10): 
(10) 
t~8 
PRED TENSE 
SUBJ 
DBJ 
'beantworten<\[Student\],\[Frage\]> r present 
I RED 'Student' 1 UMB sg END masc / f81LeREO dedJ f21~Pe c ~eF * 71 
I RED 'Frage' 1 UMB sg END fem / 
f82 \[PRED dieJJ f56~Pe c reEF + ql 
PRED ' r~pond re<\[6tudiant\], \[a\]> ° 
TENSE present 
~RED '~tudiant r\] 
IGEND MASC / 
SUBJ I NUMB sg w- +l I 
• S4LPREO I~ J 
PRED '&<\[question\]>' PCASE AOBJ 
~RED 'question r 
OBJ 1;56~ PEc ~EF +l ~85LPRED la.J 
. "~58 "C83 
The second structure is the f-structure the 
grammar of French assigns to the sentence in 
(6b). This f-structure is the input for the 
generation process. Other examples of this 
kind are pairs like like and plaire and help and 
heIfen. 
In the previous example the effects of the 
change in grammatical function between the 
source and the target language are purely 
local. In other cases there is a non-local 
dependency between the subcategorizing verb 
and a dislocated phrase. This is illustrated by 
the relative clause in (11): 
(II) (a)...der Brief, den der Student zu 
beantworten scheint. 
(b) ...la lettre, ~ laquelle l'~tudiant 
semble r~pondre. 
...the letter, that the student seemed 
to answer. 
The within-clause functions of the relativized 
phrases in the source and target language are 
determined by predicates which may be 
arbitrarily deeply embedded, but the 
relativized phrase in the target language must 
correspond to the one in the source language. 
Let us assume that relative clauses can be 
analyzed by the following slightly simplified 
phrase structure rules, making use of 
functional uncertainty (see Kaplan and 
Maxwell 1988b for a technical discussion of 
functional uncertainty) to capture the 
non-local dependency of the relativized phrase 
(equations on the head NP are ignored): 
(12) NP ~ NP S' ( I' RELADJ)= 
S t ..~ XP S 
(1' REL-TOPIC) = J, 1' = ~, ( 1` XCOMP* GF) = ~, 
We can achieve the desired correspondence 
between the source and the target by 
augmenting the first rule with the following 
transfer equations: 
(13) NP --* NP S ! ( 1` RELADJ) = 
• ~( 1` RELADJ) = (z i' RELADJ) 
z( ~ REL-TOPIC)ffi (~ ~ REL-TOPIC) 
The effect of this rule is that the ~ value of the 
relativized phrase (REL-TOPIC) in the source 
language is identified with the relativized 
phrase in the target language. However, the 
source REL-TOPIC is also identified with a 
within-clause function, say OBJ, by the 
uncertainty equation in (12). Lexical transfer 
rules such as the one given in (8) 
independently establish the correspondence 
- 277 - 
between source and target within-clause 
functions. Thus, the target within-clause 
function will be identified with the target 
relativized phrase. This necessary relation is 
accomplished by lexically and structurally 
based transfer rules that do not make reference 
to each other. 
Differences in control. A slightly more complex 
but similar case arises when the infinitival 
complement of a raising verb is translated into 
a finite clause, as in the following: 
(14) (a) The student is likely to work. 
(b) I1 est probable que l'6tudiant 
travaillera. 
In this case the necessary information is 
distributed in the following way over the 
source, target, and transfer lexicons as shown 
in Figure 2.Here the transfer projection builds 
up an underspecified target structure, to which 
the information given in the entry of probable 
is added in the process of generation. Ignoring 
the contribution of is, the f-structure for the 
English sentence identifies the non-thematic 
SUBJ of likely with the thematic SUBJ of work as 
follows: 
~8 
(15) 
~RED 'likely<\[work\]>\[student\] r 
pRED 'studentq ~UMB sg 
SUBJ flg~ PEc mEF + 3L #8~REO theJJ "~ 
pRED 'work<\[student\]>~l XCOMP f4e~USJ \[tg:student\]/ J 
The corresponding French structure in (16) 
contains an expletive SUBJ, il, for probable and 
an overtly expressed SUBJ for travaiUer. The 
latter is introduced by the transfer entry for work: 
(16) 
1;48 
~RED 
SUBJ 
COMP 
"1;46 
'probable<\[46:travailler\]>\[il\]' 
EORM iD 
~RED 'travailler<\[19:6tudiant\]> 
COMPL que 
~RED '6tudiant 
~END MASC 
SUBJ ~UMB sg 
~19~PE c~ ~EF +7 ~68~RED 1~ 
Again this f-structure satisfies the transfer 
description and is also assigned by the French 
grammar to the target sentence. 
The use of multiple projections. There is one 
detail about the example in (14) that needs 
further discussion. Simplifying matters 
somewhat, there is a requirement that the 
temporal reference point of the complement 
has to follow the temporal reference point of 
the clause containing likely, if the embedded 
verb is a process verb. Basically the same 
temporal relations have to hold in French with 
probable. The way this is realized will depend 
on what the tense of probable is, which in turn 
is determined by the discourse up to that point. 
A sentence similar to the one given in (13a) but 
appearing in a narrative in the past would 
translate as the following: 
likely A 
( 1' PRED) = 'likely<( 1' XCOMP)>( 1' SUBJ)' 
( 1` SUB J) = ( 1` XCOMP SUB J) 
probable A 
( 1` PRED) = 'probable<( 1` COUP)>( 1' SUB J)' 
( 1' SUBJ FORM) = il 
( 1' COUP COUPE) = que 
( 1' COUP TENSE) = future 
(¢1' PRED FN)=probable 
(~t COMP)=Z(1 ' XEOMP) 
Figure 2 
- 278 - 
(17) I1 6tait probable que l'dtudiant 
travaillerait. 
In the general case the choice of a French tense 
does not depend on the tense of the English 
sentence alone but is also determined by 
information that is not part of the f-structure 
itself. We postulate another projection, the 
temporal structure, reached from the 
f-structure through the correspondence X (from 
XpOVZKOS, temporal). It is not possible to 
discuss here the specific characteristics of such 
a structure. The only thing that we want to 
express is the constraint that the event in the 
embedded clause follows the event in the main 
clause. We assume that the temporal structure 
contains the following information for 
likely-to-V, as suggested by Fenstad et al. 
(1987): 
(18) likely V 
(X ? COND REL) =precede 
(X? COND ARGI)=(X? IND) 
(X ~ COND ARG2 ID)= IND-LOC2 
This is meant to indicate that the temporal 
reference point of the event denoted by the 
embedded verb extends after the temporal 
reference point of the main event. The time of 
the main event is in part determined by the 
tense of the verb be, which we ignore here. The 
only point we want to make is that aspects of 
these different projections can be specified in 
different parts of the grammar. We assume 
that French and English have the same 
temporal structure but that in the context of 
likely it is realized in a different way. This can 
be expressed by the following equation: 
(19) X 1' = X'z I' 
Here the identity between X and X-~ provides an 
interlingua-like approach to this particular 
subpart of the relation between the two 
languages. This is diagrammed in Figure 3. 
Allowing these different projections to 
simultaneously determine the surface 
structure seems at first blush to complicate the 
computational problem of generation, but a 
moment of reflection will show that that is not 
necessarily so. Although we have split up the 
different equations among several projections 
for conceptual clarity, computationally we can 
consider them to define one big attribute value 
structure with X and z as special attributes, so 
the generation problem in this framework 
reduces to the problem of generating from 
attribute-value structures which are formally 
of the same type as f-structures (see Halvorsen 
and Kaplan (1988), Wedekind (1988), and 
Momma and D6rre (1987) for discussion). 
Differences in embedding. The potential of the 
system can also be illustrated with a case in 
which we find one more level of embedding in 
one language than we find in the other. This is 
generally the case if a modifier-head relation 
in the source language is reversed in the target 
structure. One such example is the relation 
between the sentences in (20): 
(20) (a) The baby just fell. 
(b) Le b~b~ vient de tomber. 
f48 
PRED 'likely<\[work\]>\[student\] r 
~REO 'student' 7 ~ UMB sg 
floD pEc 
~RED 'work<\[studenty I XCOMP~46~UBJ \[19:student\]/ J 
)RED 
SUBJ 
COMP 
1;48 1;46 
'probable<\[travailler\])\[il\]' 
~ORM i~ 
)RED 'travailler<\[6tudiant\]> r COMPL que 
FORM finite 
~RED '6tudiant~ 
~END MASC m 
SUBJ ~UMB sg 1;1  pEc F EF +7 \[ 
1;88 REO leJ j 
I ND O0 INO-LOCI\]_ 7 ico.o IARG' II 
x48L I RG2 00  .O-LOCZDJJ 
I NO ~O IND-LOC~,.,~ 7 BE, p ece, j) 71 iCON o IARG, II 
x1;48L  RG2 00 INO-L0C /J 
Figure 3 
~-T - 279 - 
One way to encode this relation is given in the 
following lexical entry for just (remember that 
all the information about the structure of venir 
in French will come from the lexicon and 
grammar of French itself): 
(21)just ADV I: PRED)='just<() ARG)>' 
t PRED FN) -" venir (~ XCOMP) = 1;( ~ ARG) 
This assigns to just a semantic form that takes 
an ARG function as its argument and maps it 
into the French venir. This lexical entry is 
combined with phrase-structure rule (22). This 
rule introduces sentence adverbs and makes 
the f-structure corresponding to the S node fill 
the ARG function in the f-structure 
corresponding to the ADV node. 
(22) S ~ NP (ADV) VP 
(1' SUBJ)= ~ T "-(4 ARG) 
Note that the f-structure of the ADV is not 
assigned a function within the S-node's 
f-structure, which is shown in (23). This is in 
keeping with the fact that the adverb has no 
functional interactions with the material in 
the main clause. 
(23) ~RED ' fall<Ebaby\]>' q 
ITENSE past I 
m 71 
f.L f,, pEc f,o REn t, jj 
The relation between the adverb and the 
clause is instead represented only in the 
f-structure associated with the ADV node: 
(24) 
fe 
PRED 'just(\[fall\])' 
~RED 'fall<\[baby\])' 
ITENSE past 
l pREP 'baby' ARG m ~UMB sg 
ISUBJ / ~EF + " f44L 
ft8~ PEc fS0~RED th~ 
In the original formulation of LFG, the 
f-structure of the highest node was singled out 
and assigned a special status. In our current 
theory we do not distinguish that structure 
from all the others in the range of ~b: the 
grammatical analysis of a sentence includes 
the complete enumeration of dl)-associations. 
The S-node's f-structure typically does contain 
the f-structures of all other nodes as subsidiary 
elements, but not in this adverbial case. The 
target structures corresponding to the various 
f-structures are also not required to be 
integrated. These target f-structures can then 
be set in correspondence with any nodes of the 
target c-structure, subject to the constraints 
imposed by the target grammar. In this case, 
the fact that venir takes an XCOMP which 
corresponds to the ARG of just means that the 
target f-structure mapped from the ADV's 
f-structure will be associated with the highest 
node of the target c-structure. This is shown in 
(25). 
(25) ~RED 
SUBJ 
XCOMP 
¢6 
' veni r<\[tomber\]>\[b6b~\] '- 
IRE0 'beb ' l END MASC m 
UMB sg \[ 
PEC \[DEF +71~ • 141.: ~3312RED I eJJ 
~RED 'tomber<\[bebe\]>r~ 
ICOMPL de ~1 ITENSE tnf ~ II 
~23LSUBJ \[14:b6b6\]/ jj 
The above analysis does not require a single 
integrated source structure to map onto a 
single integrated target structure. An 
alternative analysis can handle differences of 
embedding with completely integrated 
structures. If we assign an explicit function to 
the adverbial in the source sentence, we can 
reverse the embedding in the target by 
replacing (22) with (26): 
(26) S --* NP (ADV) VP (Jr SADJ) = 4, 
T = (~ 4, XCOMP) 
In this case the embedded f-structure of the 
source adverb will be mapped onto the 
f-structure that corresponds to the root node of 
the target c-structure, whereas the f-structure 
of the source S is mapped onto the embedded 
XCOMP in the target. The advantages and 
disadvantages of these different approaches 
will be investigated further in Netter and 
Wedekind (forthcoming). 
CONCLUSION 
We have sketched and illustrated an approach 
to machine translation that exploits the 
potential of simultaneous correspondences 
between different levels of linguistic 
representation. This is made possible by the 
equality and description based mechanisms of 
LFG. This approach relies mainly on 
codescription, and thus it is different from 
other aFG-based approaches that use a 
- 280- 
description-by-analysis mechanism to relate 
the f-structure of a source language to the 
f-structure of a target language (see for 
example Kudo and Nomura, 1986). Our 
proposal allows for partial specifications and 
multi-level transfer. In that sense it also 
differs from strategies pursued for example in 
the Eurotra project (Arnold and des Tombe, 
1987), where transfer is based on one level of 
representation obtained by transforming the 
surface structure in successive steps. 
We see it as one of the main advantages of 
our approach that it allows us to express 
correspondences between separate pieces of 
linguistically motivated representations and 
in this way allows the translator to exploit the 
linguistic descriptions of source and target 
language in a more direct way than is usually 
proposed. 
ACKNOWLEDGEMENTS 
Thanks to P.-K. Halvorsen, U. Heid, H. Kamp, 
M. Kay and C. Rohrer for discussion and 
comments. 
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