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<Paper uid="J87-3009">
  <Title>THE SELF-EXTENDING PHRASAL LEXICON*</Title>
  <Section position="31" start_page="0" end_page="0" type="concl">
    <SectionTitle>
12. CONCLUSIONS
</SectionTitle>
    <Paragraph position="0"> We have shown how the Dynamic Hierarchical Phrasal Lexicon (DHPL) supports language analysis, and language acquisition. We accounted for a dynamic language behavior by promoting four aspects of lexical representation: Phrases: The lexicon contains entire phrases, accounting uniformly for an entire range including productive as well as non-productive phrase.</Paragraph>
    <Paragraph position="1"> Hierarchy: The lexicon organizes in a hierarchy, phrases ranging from specific &amp;quot;lexical entries&amp;quot; at the bottom, to general &amp;quot;grammar rules&amp;quot; at the top. Lexical Presupposition: Contextual conditions are incorporated into the lexicon through lexical presuppositions. Presuppositions account for disambiguation in parsing, and for phrase selection in generation.</Paragraph>
    <Paragraph position="2"> Integration of Syntax and Semantics: Phrases specify a relation (in the logical sense) between syntax and semantics. Thus, the question whether any lexical feature is syntax or whether it is semantics, becomes insignificant. For example, consider thematic roles for a phrase such as promise (Section 6.4). Are they syntactic or are they semantic? They can be viewed as either.</Paragraph>
    <Paragraph position="3"> Using this representation we have shown three results in language processing: Coping with Lexical Gaps: The hierarchical structure of the lexicon enables parsing of text even when certain lexical elements are unknown. A partial meaning for the text, which serves as an initial hypothesis, is formed by applying general knowledge when specific knowledge is missing.</Paragraph>
    <Paragraph position="4"> Using Lexical Clues: In learning meanings of phrases we have used &amp;quot;linguistic clues&amp;quot;. For instance, the word at in the judge threw the book at AI, supports the learning process of that idiom. What is the justification for drawing inferences from apparently vague senses of words? In making the lexicon amenable as a linguistic database, from which inference rules can be drawn, we have systematically organized words in a hierarchy, representing words such as at, to, around and away.</Paragraph>
    <Paragraph position="5"> Thus, the use of linguistic clues per se is not inappropriate; however, all linguistic clues used in a reasoning system, must be drawn from a well-organized lexicon.</Paragraph>
    <Paragraph position="6"> Knowledge Propagation through Generalization and Specialization: Hierarchy is a precondition for learning by generalization. Through the hierarchical scheme, there are two ways of propagating knowledge: First, bottomup-from instantiated episodes up towards specific phrases, and even higher to generalized word senses.</Paragraph>
    <Paragraph position="7"> Second, top-down-generalized word senses are propagated down for prediction of new specific phrases. In both cases, effective learning depends on the existence of a well refined hierarchy. Any linguistic system must accommodate not only for spanning a static language, but also for augmenting the original linguistic system itself. In DHPL we have shown how, for a variety of linguistic features, the lexicon itself can be augmented through linguistic experiences. Thus we have accomplished a dynamic linguistic behavior.</Paragraph>
  </Section>
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