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<Paper uid="P06-1107">
  <Title>using selectional preferences</Title>
  <Section position="3" start_page="0" end_page="849" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Natural Language Processing applications often need to rely on large amount of lexical semantic knowledge to achieve good performances. Asymmetric verb relations are part of it. Consider for example the question &amp;quot;What college did Marcus Camby play for?&amp;quot;. A question answering (QA) system could find the answer in the snippet &amp;quot;Marcus Camby won for Massachusetts&amp;quot; as the question verb play is related to the verb win. The vice-versa is not true. If the question is &amp;quot;What college did Marcus Camby won for?&amp;quot;, the snippet &amp;quot;Marcus Camby played for Massachusetts&amp;quot; cannot be used. Winnig entails playing but not vice-versa, as the relation between win and play is asymmetric.</Paragraph>
    <Paragraph position="1"> Recently, many automatically built verb lexical-semantic resources have been proposed to support lexical inferences, such as (Resnik and Diab, 2000; Lin and Pantel, 2001; Glickman and Dagan, 2003). All these resources focus on symmetric semantic relations, such as verb similarity. Yet, not enough attention has been paid so far to the study of asymmetric verb relations, that are often the only way to produce correct inferences, as the example above shows.</Paragraph>
    <Paragraph position="2"> In this paper we propose a novel approach to identify asymmetric relations between verbs. The main idea is that asymmetric entailment relations between verbs can be analysed in the context of class-level and word-level selectional preferences (Resnik, 1993). Selectional preferences indicate an entailment relation between a verb and its arguments. For example, the selectional preference {human} win may be read as a smooth constraint: if x is the subject of win then it is likely that x is a human, i.e. win(x) - human(x). It follows that selectional preferences like {player} win may be read as suggesting the entailment relation win(x) - play(x).</Paragraph>
    <Paragraph position="3"> Selectional preferences have been often used to infer semantic relations among verbs and to build symmetric semantic resources as in (Resnik and Diab, 2000; Lin and Pantel, 2001; Glickman and Dagan, 2003). However, in those cases these are exploited in a different way. The assumption is that verbs are semantically related if they share similar selectional preferences. Then, according to the Distributional Hypothesis (Harris, 1964), verbs occurring in similar sentences are likely to be semantically related.</Paragraph>
    <Paragraph position="4"> The Distributional Hypothesis suggests a generic equivalence between words. Related methods can then only discover symmetric relations. These methods can incidentally find verb pairs as (win,play) where an asymmetric entailment relation holds, but they cannot state the direction of entailment (e.g., win-play).</Paragraph>
    <Paragraph position="5"> As we investigate the idea that a single relevant verb selectional preference (as {player}  win) could produce an entailment relation between verbs, our starting point can not be the Distributional Hypothesis. Our assumption is that some point-wise assertions carry relevant semantic information (as in (Robison, 1970)). We do not derive a semantic relation between verbs by comparing their selectional preferences, but we use point-wise corpus-induced selectional preferences.</Paragraph>
    <Paragraph position="6"> The rest of the paper is organised as follows.</Paragraph>
    <Paragraph position="7"> In Sec. 2 we discuss the intuition behind our research. In Sec. 3 we describe different types of verb entailment. In Sec. 4 we introduce our model for detecting entailment relations among verbs . In Sec. 5 we review related works that are used both for comparison and for building combined methods. Finally, in Sec. 6 we present the results of our experiments.</Paragraph>
  </Section>
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