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<Paper uid="E93-1024">
  <Title>Restriction and Correspondence-based Translation</Title>
  <Section position="2" start_page="0" end_page="194" type="intro">
    <SectionTitle>
1. Introduction
</SectionTitle>
    <Paragraph position="0"> Kaplan et al. (1989) present a framework for translation based on the description and correspondence concepts of Lexical-Functional Grammar (Kaplan and Bresnan, 1982). LFG formulates the syntactic dependencies and generalizations of natural languages in terms of the properties of formal structures of different types: ordinary phrase-structure trees represent the surface constituency of sentences while hierarchical finite functions represent their underlying grammatical relations. The structures for a particular sentence are those that satisfy descriptions produced from annotated phrase-structure rules and lexical entries. The description of the more abstract functional structure is determined by the dominance and precedence relations of the superficial constituent structure, given the assumption that there is a piecewise correspondence function that maps the nodes in the c-structure tree into the units of the f-structure. Kaplan (1987) and Halvorsen and Kaplan (1988) extend this structure/description/correspondence architecture to provide modular and declarative characterizations of the relationships between syntactic structures and other levels of linguistic representation. Kaplan et al. (1989) suggest that this architecture can provide a formal basis for specifying complex source-target translation relationships in a declarative fashion that builds on monolingual grammars and lexicons that are independently motivated and theoretically justified. In particular, the approach permits features from different linguistic levels to affect translation without requiring that reflexes of those disparate features appear together in an otherwise unmotivated transfer or interlingual representation.</Paragraph>
    <Paragraph position="1"> Kaplan et al. (1989) offer several examples to illustrate the effectiveness of this approach to translation. These examples involve changes in grammatical functions from source to target, differences in control, and differences in embedding (or head-switching). The Kaplan et al. solutions depend on monolingual representations of phrasal, functional, and semantic information related by the correspondences ~p and a, with translation  correspondences * and ~' mapping source to target structures, as shown in the configuration in (1):</Paragraph>
    <Paragraph position="3"> These solutions utilize the formal device of codescription to specify the target structure constraints in terms of simple compositions of the and z' mappings with the monolingual source correspondences. For instance, the fact that the object of the German beantworten corresponds to the AOBJ of the French r~pondre is indicated by associating the following transfer equations with the normal monolingual lexical entry for beantworten: (2) (~ ~ PRED FN) = rdpondre</Paragraph>
    <Paragraph position="5"> The last line asserts that the AOBJ in the target f-structure is the translation of the source OBJ.</Paragraph>
    <Paragraph position="6"> The metavariable ~ in LFG is an abbreviation for (1)(M(*)) and thus denotes the f-structure that corresponds to the mother of the beantworten lexical node in the German c-structure (indicated by *). The expression * ~ can then be seen as ~(~(M(*))) = ~ o ~b(M(*)) and thus as incorporating the composition ~odp. Significantly, the M(*) term is also present, which means that the target constraints are determined in the same recursive analysis of the source c-structure that is used to derive the source f-structure description. The codescription device crucially involves both a composition of correspondences and a single recursive analysis of common ancestor structures. This contrasts with descriptionby-analysis, another technique mentioned by Kaplan and Halvorsen (1988) and Kaplan et aL (1989) for deriving descriptions of abstract structures.</Paragraph>
    <Paragraph position="7"> 2. Difficulties with the correspondence approach This proposal for correspondence-based translation has been scrutinized by a number of researchers (e.g. Sadler et al., 1989, Sadler et al., 1990, Sadler and Thompson, 1991), and several difficulties have been pointed out. These difficulties arise particularly in cases where the independently motivated source and target structures are not very closely aligned, where single units in a source structure map to multiple units in the target (so-called splitting) or where hierarchical relationships are interchanged in mapping from source to target (switching). If such discrepancies are both locally bounded and predictable, then they can in principle be handled by means of codescription statements involving the ordinary monolingual description-language constructs of function-application and equality.</Paragraph>
    <Paragraph position="8"> But even if possible, such conservative treatments may not permit obvious generalizations about the translation relation to be naturally expressed. Sadler et al. (1990) demonstrate this point by examples in which the translation of a lexical head differs according to its dependents in the source sentence (English commit suicide translates to French (se) suicider whereas commit a crime translates to commettre une crime). They suggest refining the basic correspondence approach by separating such idiosyncratic source-target interactions into a separate transfer lexicon whose stipulations will override (perhaps via the priority union operator) the generic transfer specifications that might still be associated with the source-language predicates.</Paragraph>
    <Paragraph position="9"> Sadler et al. (1989) and Sadler and Thompson (1991) focus on another case of structural misalignment in translation, as illustrated in (3):  (3) (a) The baby just fell.</Paragraph>
    <Paragraph position="10"> (b) Le b~b~ vient de tomber.</Paragraph>
    <Paragraph position="11">  The syntactic head of the English sentence (fell) corresponds to the head of the French embedded complement (tomber), while the English adjunct just corresponds to the head of the French matrix. Other well-known contrasts show syntactic embeddings in English corresponding to sentential adjuncts in Dutch (and German):  (4) (a) John likes to swim.</Paragraph>
    <Paragraph position="12"> (b) Janzwemt graag.</Paragraph>
    <Paragraph position="13">  Kaplan et al. (1989) discussed such differences in embedding and offered two alternative analyses that rely only on codescriptive specifications. On one account, head-switching is accomplished by mapping the source S node to an f-structure that contains information about the central clausal relations but excludes adjunct information. The ADV node maps to an f-structure that has the adverb as its main predicate with the central clausal f-structure appearing in argument position. The 'just' f-structure, though not accessible from the S node, maps through t to the outermost target f-structure. This complex interchange is specified in the lexical entry and rule in (5) and is diagrammed in Figure 1  (ignoring such details as person, number, case, and tense).</Paragraph>
    <Paragraph position="14"> (5) (a) just ADV (1` PRED)='just&lt;(I' ARG)&gt;' (1; 1' PRED FN)=venir (~ 1` XCOMP)-----~( 1' ARG) (b) S -~ NP (ADV) VP</Paragraph>
    <Paragraph position="16"> In the second proposal a completely integrated source f-structure maps to a single integrated target structure. As specified by the rule (6), the adverb is assigned an adjunct grammatical function in the source and its translation includes the translation of the enclosing source f-structure as its XCOMP, as shown in Figure 2.</Paragraph>
    <Paragraph position="18"> Sadler et aI. (1989) and Sadler and Thompson (1991) point out a significant inadequacy of both these arrangements. Even though the proper target embeddings are derived under both correspondence configurations, in neither case does the translation of the f-structure of the source S node include the translation of the adverb. This shows up as a problem when such examples are embedded as complements in larger sentences:  (7) (a) I think that the baby just fell.</Paragraph>
    <Paragraph position="19"> (b) Je pense que le bdbd vient de tomber.</Paragraph>
    <Paragraph position="20">  To maintain modularity, the codescriptive lexical entry for think must provide a direct mapping to the French penser that is not sensitive to the internal structure of the complement, along the</Paragraph>
    <Paragraph position="22"> But then the translation f-structure constraints will characterize the pair of structures (9); these share the common tomber substructure but are otherwise unrelated.</Paragraph>
    <Paragraph position="23">  The z constraints thus leave unspecified the relative scopes of the penser and venir predicates. As Sadler et al. (1989) observe, the problem is even worse when several adverbs appear together: there is no obvious way to modify either of the rules (hb) or (6) to account for the scope interactions among the adverbs, let alone their relations to higher predicates.</Paragraph>
    <Paragraph position="24"> Sadler et al. (1989) and Sadler and Thompson (1991) consider several ways in which the translation constraints might be modified to circumvent these difficulties yet remain faithful to the spirit of the correspondence-based approach. While each of their proposals is carefully worked out, they conclude (and we agree) that none of them is completely satisfactory or particularly compelling. The reason, we believe, is that the head-switching with adverbial modifiers that shows up as a problem in correspondence-based translation is actually a symptom of a more fundamental error in the syntactic and semantic analysis of the source language. In sentences with adverbial modifiers, the syntactic head (which controls subcategorization and enters into agreement relations) is not the same as the semantic head (the predicate with widest scope). Moreover, normal linguistic arguments would assign a flat f-structure to sentences with several adverbs while meaning relations would be represented in a hierarchical semantic structure. Thus on this view, if translation codescriptions map from the proper hierarchical semantic structures via ~' instead of from flat f-structures via ~, adverbial head-switching disappears as a special problem for correspondence-based translation.</Paragraph>
    <Paragraph position="25"> Sadler and Thompson (1991, footnote I) mention the arrangement we are proposing, and observe that the translation codescription problems may then merely be displaced to equivalent difficulties in characterizing the monolingual o instead of z: the problems may be moved around and renamed, but not solved. This may be so, but any conceptual clarification in such a murky domain must be regarded as an advance, if only because it helps to spotlight the issues that are relevant to a solution and to connect them to other related phenomena.</Paragraph>
    <Paragraph position="26"> Indeed, we now suggest that adverbial head-switching is a special case of the general problem of mapping flat syntactic structures to hierarchical semantic ones. So-called &amp;quot;light verbs&amp;quot;, complex-predicates, and clause-union phenomena in many languages are similarly difficult to handle in LFG using only codescription, attribute-value functionapplication, and equality constraints (or using the analogous formal devices of other theories, such as attribute-value unification over signs or categories). In the next section of this paper, we extend LFG's f-structure description language by introducing a new formal operator, called restriction. We illustrate its properties by applying it to a simple light-predicate sentence in Urdu. In Section 4 we combine restriction with description-by-analysis to characterize the appropriate hierarchical semantic structures for English sentential adverbs. At the end, we return to the head-switching problem of correspondence-based translation, providing a simple solution in terms of the ~' correspondence.</Paragraph>
  </Section>
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