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<Paper uid="W91-0222">
  <Title>A Two-Level Knowledge Representation for Machine Translation: Lexical Semantics and Tense/Aspect</Title>
  <Section position="4" start_page="258" end_page="260" type="metho">
    <SectionTitle>
3 Classification of Connectives: Cross-Linguistic Ap-
</SectionTitle>
    <Paragraph position="0"> plicability The when construction has been studied extensively in the literature. In particular, it has been noticed that the aspectual properties of the clauses conjoined by when often change the temporal meaning of the entire sentence. (See \[Moens and Steedman, 1988\] and \[Yip, 1985\] among others.) Allen's temporal logic falls short in this regard: it does not capture well-known patterns of tense implications based on aspectual distinctions. 9 Some examples of when constructions (taken from \[Yip, 1985\]) are shown here: 1deg (Note that the word when potentially maps to more than one temporal relation if we adopt Allen's framework.)  (19) Simple process with simple event: &gt;, =, mi John left when Mary axrived.</Paragraph>
    <Paragraph position="1"> (20) Progressive process with simple event: di, fi John was leaving when Mary arrived.</Paragraph>
    <Paragraph position="2"> (21) Simple state with simple event: mi, si, di, m, &gt;, &lt;, = John was angry when Mary arrived.</Paragraph>
    <Paragraph position="3"> (22) Progressive process with progressive event: =, f, fi, s, si, d, di, o, oi  As it turns out, the temporal relations enumerated in figure 4 for the when connective cover the cases shown here, plus many others that are not addressed by Yip. There are two important advantages to using the featural scheme of figure 4 over the less specific scheme of \[Yip, 1985\]: (1) it provides a more precise specification of states and events; and (2) it includes temporal/aspectual information that is important for the realization of other types of surface-structure constituents (besides temporal connectives) such as the number of a verbal object. We will return to this second point shortly. Although the when construction has been studied extensively, it has not been examined in the context of machine translation. In particular, the question of whether the tense/aspect theories of Allen, Bennett, et al., Dowty, Reichenbach, Vendler, and others can be combined to provide a cross-linguistic account for the selection of tense/aspect and temporal connectives such as when (e.g., in an interlingual translation model) has not been addressed.</Paragraph>
    <Paragraph position="4"> Machine translation provides an appropriate testbed for trying out such theories. The problem of lexical selection during generation of the target language is the most crucial issue in this regard. For example, one must choose between the lexical tokens cuando and al when generating an equivalent Spanish temporal connective for the following two English sentences: (23) (i) John went to the store when Mary arrived.</Paragraph>
    <Paragraph position="5"> (ii) John had gone to the store when Mary arrived.</Paragraph>
    <Paragraph position="6"> In the case of (23)(i), there are two possible translations, one that uses the connective cuando, and one that uses the connective al: (24) (i) Juan rue a la tienda cuando Marfa lleg6.</Paragraph>
    <Paragraph position="7"> (ii) Juan fue a la tienda al llegar Marfa.</Paragraph>
    <Paragraph position="8"> Either one of these sentences is an acceptable translation for (23)(i). However, the same is not true of (23)(ii)? 1 (25) (i) Juan habfa ido a la tienda cuando Marfa lleg6.</Paragraph>
    <Paragraph position="9"> (ii) Juan habfa ido a la tienda al llegar Marfa.</Paragraph>
    <Paragraph position="10"> Sentence (25)(i) is an acceptable translation of (23)(ii), but (25)(ii) does not mean the same thing as (23)(ii). This second sentence implies that John has already gone to the store and come back, which is not the preferred reading.</Paragraph>
    <Paragraph position="11"> Currently research is under way to enumerate all of the English temporal connectives (taken from Webster's on-line dictionary) in order to establish an association between these connectives and the aspectual interpretation for the matrix and adjunct events (in the manner shown in figure 4). These tables vary from language to language, but the procedure for choosing temporal connectives applies cross-linguistically once the tables for each language are compiled. For example, the table for the Spanish connective al would be similar to the table for the English connective when in figure 4 except that the specification for the &amp;quot;&lt;&amp;quot; relation would require the matrix event to have the +relic feature (i.e., the matrix action must reach a culmination). Thus, the full type entry under the matrix clause for the word al would be \[:kd,+t,:ka\]. This would account for the distinction between cuando and al in sentences (25)(i) and (25)(ii) above.</Paragraph>
    <Paragraph position="12"> Space limitations do not permit the enumeration of the other temporal connective tables. Some examples of connectives that are currently being compiled into tables are: after, as soon as, at the moment that, before, between, during, since, so long as, until, 11I am indebted to Jorge Lobo for pointing this out to me.</Paragraph>
    <Paragraph position="13">  while, etc. It is intended that these tables are to be used both for the selection of temporal connectives during the generation process (for which the relevant index into the tables would be the temporal relation and the lexical-semantic types encoded in the interlingua) and for temporal interpretation during the analysis process (for which the relevant index into the tables would be the lexical-semantic types and aspectual perspectives associated with the source-language sentence). The selection of a temporal connective, then, is simply a table look-up procedure based on the type of the events and the temporal interpretation that holds between the events. For example, if we had a \[+d,-t,-a\] event E1 (e.g., run) and a \[+d,+t,+a\] event E2 (e.g., arrive), and if we knew that the temporal relation between E1 and E~ was m, then searching the when table would fail, but searching the until table would succeed, thus allowing a sentence such as John ran until Mary arrived to be generated.</Paragraph>
    <Paragraph position="14"> As mentioned earlier, the featural system outlined above provides a framework that is appropriate not only for the realization of temporal connectives, but also for the realization of other types of temporal/aspectual information. For example, the sentence I stabbed Mary could he realized in at least two ways in Spanish: (26) (i) Juan le dio pufialadas a Marla (ii) Juan le dio una pufialada a Marla Both of these sentences translate literally to &amp;quot;John gave stab wound(s) to Mary.&amp;quot; However, the first sentence is the repetitive version of the action (i.e., there were multiple stab wounds), whereas the second sentence is the non-repetitive version of the action (i. e., there was only one stab wound). This distinction is characterized by means of the atomicity feature. In (26)(i), the event is associated with the features \[+d,+t,-a\], whereas, in (26)(ii) the event is associated with the features \[+d,+t,+a\]. According to \[Bennett et al., 1990\] (in the spirit of \[Moens and Steedman, 1988\]), predicates are allowed to undergo an atomicity &amp;quot;coercion&amp;quot; in which an inherently non-atomic predicate (such as dio) may become atomic under certain conditions. These conditions are language-specific in nature, i.e., they depend on the lexical-semantic structure of the predicate in question. Given the featural scheme that is imposed on top of the lexical-semantic framework, it is easy to specify coercion functions for each language. For example, the atomicity function for the stab example would specify that a singular NP verbal object maps a \[+d,-a\] predicate into a \[+d,+a\] predicate i.e., a non-atomic event becomes atomic if it is associated with a singular NP object. Thus, the notion of feature-based coercion is cross-linguistically applicable, providing a useful foundation for a model of interlingual machine translation.</Paragraph>
  </Section>
  <Section position="5" start_page="260" end_page="261" type="metho">
    <SectionTitle>
4 Extension of the Temporal/Aspectual Framework
</SectionTitle>
    <Paragraph position="0"> to the Spatial Domain In addition to investigating the cross-linguistic applicability of the temporal/aspectual framework in the context of machine translation, current research is under way to extend the representation to the spatial domain. This possibility has also been investigated by \[Mukerjee and Joe, 1990\], in which the interval logic model of \[Allen, 1983\] has been extended to be applicable to the spatial domain. For example, the one-dimensional interval relation C(++)B specifies that the spatial interval C is, in some sense, &amp;quot;after&amp;quot; the spatial interval B. This relation is analogous to Allen's temporal relation C &gt; B, which specifies that the temporal interval C occurs after the temporal interval B. Other spatial relations  that are currently under investigation are: above, before, behind, between, beyond, down, following, nezt to, off, on, to, under, within, etc. It is expected that the principles that govern the relation of temporal primitives to lexical items will hold for analogous primitives in the spatial field; experiments are currently being conducted to test this hypothesis.</Paragraph>
  </Section>
  <Section position="6" start_page="261" end_page="261" type="metho">
    <SectionTitle>
5 Summary
</SectionTitle>
    <Paragraph position="0"> This paper has examined a two-level knowledge representation model for machine translation that integrates the tense and aspect information based on theories by both Hornstein (in the spirit of Reichenbach) and Allen with lexical-semantic information based on theories by Jackendotf in the spirit of Dowty and Vendler. We have examined the question of cross-linguistic applicability showing that the integration of tense and aspect with lexical-semantics is especially critical in machine translation when there are a number of temporal/aspectual possibilities that may be generated from a lexical semantic representation. Finally, we have discussed the possibility of extending the temporal notation to the spatial domain.</Paragraph>
  </Section>
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