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<Paper uid="C94-2121">
  <Title>Word Sense i)ismnl}iguati&lt;)n and Text Set mentation</Title>
  <Section position="3" start_page="0" end_page="755" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> A text is not a mere set of unrelated sentences.</Paragraph>
    <Paragraph position="1"> Rather, sentences in a text are about the same thing and connected to each other\[l()\]. Cohesion and cohere'nee are said to contribute to such connection of the sentences. While coherence is a semantic relationship and needs computationally expensive processing for identification, cohesion is a surface relationship among words iu a text and more accessible than coherence. Cohesion is roughly classitled into reference t, co'r@tnction, and lezical coh, esion 2.</Paragraph>
    <Paragraph position="2"> Except conjmwtion that explicitly indicates l;he relationship between sentences, l;he other two &lt;:lasses are considered to t&gt;e similar in that the relationship hetweer~ sentences is in&lt;licated by two semantically same(or related) words. But lexical  sion in Ilalllday and Hasan's classillcation a.re included here.</Paragraph>
    <Paragraph position="3"> cohesion is far easier to idenlAfy than reference because 1)oth words in lexical cohesion relation appear in a text while one word in reference relation is a pr&lt;mom, or elided and has less information to infer the other word in the relation automatically. Based on this observation, we use lexical cohesion as a linguistic device for discourse analysis. We call a sequence of words which are in lexieal cohesion relation with each other a Icxical chain like \[10\]. l,exical chains tend to indicate portions of a text; that form a semantic uttit. And so vari.ous lexical chains tend to appear in a text corre. spou(ling to the change of the topic. Therefore, I. lexical chains provide a local context to aid in the resolution of word sense ambiguity; 2. lexical &lt;'hains provide a &lt;'lue for the determination of segnlent boundaries of the text\[10\]. \]n this paper, we first describe how word sense ambiguity can t)e resolved with the aid of lexical cohesion. During the process of generating lexi&lt;'al chains incrementally, they are recorded in a register in the order of the salience. The salie'ncc of lexical chains is based on their recency and length. Since the more salient lexical chain rep resents the nearby local context, by checking lexi: ca\[ cohesion between the current word and lexieal chains in the order of tile salience, in tandem with generatiou of lexical chains, we realize incremen.</Paragraph>
    <Paragraph position="4"> tal word sense disambiguation based on contextual information that lexical chains reveal.</Paragraph>
    <Paragraph position="5"> Next;, we describe how segment boundaries of a text can be determined with the aid of lexical cohesion. Since the start and end points of lexical chains it, the text tend to indicate the start and end points of the segment, we can measure the plausibility o\[' each point in the text as a segment boundary by computing a degree of agreement of the sta.rt and end points of lexical chains.</Paragraph>
    <Paragraph position="6">  Morris and Itirst\[10\] pointed out the above two importance of lexical cohesion for discourse analysis and presented a way of computing lexical chains by using Roger's International Thesaurus\[15\]. IIowever, in spite of their mention to the importance, they did not present the way of word sense disambiguation based on lexical cohesion and they only showed the correspondences between lexical chains and segment boundaries by their intuitive analysis.</Paragraph>
    <Paragraph position="7"> McRoy's work\[8\] can be considered as the one that uses the information of lexical cohesion for word sense disambiguation, but her method does not; take into account the necessity to arrange lexical chains dynamically. Moreover, her word sense disambignation method based on lexical cohesion is not evaluated fully.</Paragraph>
    <Paragraph position="8"> In section two we outline what lexical cohesion is. In section three we explain the way of incremental generation of lexical chains in tandem with word sense disambiguation and describe the result of the evaluation of our disambiguation method. In section four we explain the measure of the plausibility of segment boundaries and describe the result of the evaluation of our measure.</Paragraph>
  </Section>
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