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<Paper uid="J98-3003">
  <Title>A Generative Perspective on Verb Alternations</Title>
  <Section position="2" start_page="0" end_page="0" type="abstr">
    <SectionTitle>
1. Introduction
</SectionTitle>
    <Paragraph position="0"> In this paper, we approach the problem of verb alternations from the perspective of knowledge-based natural language generation (NLG), which aims at producing a set of verbalizations from a common underlying representation. This viewpoint places some specific requirements on the nature of lexical representations, which will be explained in Section 2. Thereafter, we will investigate the problem of systematically generating a number of verb alternations--a problem that so far has received little attention in the NLG community.</Paragraph>
    <Paragraph position="1"> Why should a language generator have knowledge about producing alternations? Because a sophisticated discourse production may call for using a verb in one or another configuration, depending on the current situation of utterance. Alternations can place the emphasis on different elements of the sentence, and distribution of emphasis is influenced by the development of the discourse--and thus related to a whole range of other generation decisions. To illustrate, consider the following alternative beginnings of a little story:  (1) (a) Tom was in a hurry, but he had to change the oil before hitting the road. He crawled under the car and unscrewed the drain bolt. The engine drained in 20 seconds ....</Paragraph>
    <Paragraph position="2"> (b) Time was short, but the oil had to be changed before Tom could hit the road. Within 20 seconds, he drained the engine. Then ...</Paragraph>
    <Paragraph position="3"> (c) Tom was in a hurry, but he had to change the oil before hitting the  road. Quickly, he crawled under the car and unscrewed the drain bolt.</Paragraph>
    <Paragraph position="4"> For 20 long seconds, the oil drained from the engine ....</Paragraph>
    <Paragraph position="5">  * TU Berlin, FB Informafik, Sekr. FR 6--10, Franklinstr. 28/29, 10587 Berlin, Germany (~) 1998 Association for Computational Linguistics Computational Linguistics Volume 24, Number 3 (d) Tom was in a hurry, but he had to change the oil before hitting the road. Crawling under the car, he drained the old oil from the engine, and  then...</Paragraph>
    <Paragraph position="6"> Depending on how the story develops, which might hinge on stylistic parameters, a different configuration of to drain, with different subjects, objects, and prepositional phrases, should be produced. Therefore, if an NLG system is expected to be able to cope with such differences, it needs knowledge of what alternations are possible for a given verb, and how the different syntactic configurations relate to differences in meaning.</Paragraph>
    <Paragraph position="7"> In linguistics, the central goal of research on alternations is to uncover the relationships between syntax and semantics (linking rules), and to form classifications of verbs according to their alternation behavior (Levin 1993). To accomplish these goals, the need for fine-grained lexical-semantic representations is pointed out, although there is no strong consensus yet on exactly what such representations should look like (see the discussion in Levin and Rappaport Hovav \[1995, chapter 1\]). NLG, in any case, needs representations to work with; and in order to account for verb alternations, we need to devise rather fine-grained ones. In particular, a generator has to relate the (possible) changes in meaning to the changes in form, so that--from a given representation--the correct set of &amp;quot;alternated verb forms&amp;quot; can be produced. In other words, the generator needs to know the conditions under which some input representation licenses the use of a specific alternation.</Paragraph>
    <Paragraph position="8"> As a step in this direction, we consider a number of alternations that affect the aspectual category (or Aktionsart) of the verb--a group that Levin (1993, 12) chose not to focus on. We look at the differences in meaning that coincide with such alternations, and propose suitable representations for input specifications (the underlying ontology), for verb meaning, and for the alternation rules. These rules are able to sequentially derive the various alternated forms from a single base form, which is stated in the lexical entry. The approach has been implemented in a bilingual generation system, which can produce the &amp;quot;alternated paraphrases&amp;quot; in English and German. To demonstrate its capabilities, we will show how a salience parameter associated with the input can give rise to selecting one or another of the alternatives; specifically, the production of the alternative drain sentences (1a-d), from a common underlying representation, will be demonstrated.</Paragraph>
    <Paragraph position="9"> The paper is organized as follows: Section 2 discusses the specific requirements of lexical information in NLG, focusing on verbs, and suggests a format for dictionary entries. Section 3 develops our approach to verb alternations and proposes rules that account for several such alternations. Section 4 describes the implementation of the alternation framework in the Moose generator, and Section 5 concludes and compares our approach to related research. While Sections 2 and 3 are concerned with linguistic representations and make only little reference to NLG, Section 4 presupposes some knowledge of the generation concepts and systems that Moose is built upon.</Paragraph>
  </Section>
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