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<Paper uid="P79-1003">
  <Title>WORD EXPERT PARSING l</Title>
  <Section position="1" start_page="0" end_page="0" type="abstr">
    <SectionTitle>
WORD EXPERT PARSING l
</SectionTitle>
    <Paragraph position="0"> This paper describes an approach to conceptual analysis and understanding of natural language in which linguistic knowledge centers on individual words, and the analysis mechanisms consist of interactions among distributed procedural experts representing that knowledge. Each word expert models the process of diagnosing the intended usage of a particular word in context. The Word Expert Parser performs conceptual analysis through the Interactlons of tl~e individual experts, which ask questions and exchange information in converging on a single mutually acceptable sentence meaning. The Word Expert theory is advanced as a better cognitive model of natural language understanding than the traditional rule-based approaches. The Word Expert Parser models parts o~ tSe theory, and the important issues of control and representation that arise in developing such a model \[orm the basis of the technical discussion. An example from the prototype LISP implementation helps explain the theoretical results presented.</Paragraph>
    <Paragraph position="1"> \[. Introduction Computational understanding of natural language requires complex Interactions among a variety of distinct yet redundant mechanisms. The construction of a computer program to perform such a task begins with the development of an organizational framework which Inherently .incorporates certain assumptions about the nature ot these processes and the environment in which they take place. Such cognitive premises affect nro?oundly the scope and substance of computational ~nalysis for comprehension as found in the program.</Paragraph>
    <Paragraph position="2"> This paper describes a theory of conceptual parsing which considers knowledge about language to be distributed across a collection of procedural experts centered on individual words. Natural language parsing with word experts entails several new hypotheses about the organization and representation of linguistic and pragmatic knowledge for computational language comprenension. The Word Expert Parser \[1\] demonstrates hpw the word expert qTt~T~ed wPS~h certain ocher choices oaseo on previous work, affect structure and process in a cognitive model of parsing.</Paragraph>
    <Paragraph position="3"> The Word Expert Parser is a cognitive model of conceptual language analysis in which the unit of ltngu~stic knowledge is the word and the fqcu~ o~ research ts the set or processes unoerlyinR comprehension. The model is aimed directly at problem~ of word sense ambiguity and idiomatic expressions, and in greatly generalizing the notion of wora sense, promotes these issues to a central place in the study of language parsing. Parsing models typically cope unsatisfactorily with the wide heterogeneity of usages of particular words. If a sentence contains a standard form of a word, it can usually be parsed; if it involves a less prevalent form which has a different part of speech, perhaps it too can be parsed. Disti.nguishing amen 8 the ~any senses of a common vero, adjective, or pronoun, tar example, or correctly translating idioms are rarely possible, At the source of this difficulty is the reliance on rule-based formalisms, whethar syntactic or semantic (e.g.. cases), which attempt to capture ~he linguistic contributions inherent in constituent chunks or sentences that consist of more than single words. A crucial assumption underlying work on the Word Expert Parser is that the ~undamental unit of linguistic Knowledge is the word. and that understanding its sense or role in a particular context is the central parsing process. In the parser to be described, the word expert constitutes the kernel of linguistic knowled~nd zts representation the e~emental data structure. IE is procedural in nature and executes directly as a process, cooperating with the other experts for a given sentence to arrive at a mutually acceptable sentence meaning.</Paragraph>
    <Paragraph position="4"> Certaln principles behind the parser d 9 nqt follow directly from the view or worn primacy, out ~rom other recent theories of parsing. The cognitive processes involved in language comprehension comprise the focus of linguistic study of the word expert approach. Parsin8 is viewea as an inferential process where linguistic knowledge of syntax and semantics and general pragmatic knowledge are applied in a uniform manner during IThe research described in this renor~ .is funded by the National Aeronautics and Space Admzn~stratton under grant , n umbe, r NSC-7255. Their support is gratefully acKnowleageG, Interpretatlon. This methodological position closely follows that of Rlosbeck (see \[2\] and \[3 \]) and Schank \[4\]. The central concern with word usage and word sense ambiguity follows similar motivatlons of Wllks \[5\]. The control structure of the Word Expert Parser results from agreqment .with ~he hypothesis of .Harcus that parsing can he none aetermzntsttcally and ~n a way tn Dhlcn information ,gained through interpretation is permanent \[6\]. Rieger ~ view of inference as intelligent secectlon tmong a number of competing plausible alternatives {7J of course forms the cornerstone of the new theory. Hi~ ideas on word sense selection for language analysis (\[8\] and \[9~) and strategy selection for general problem solving \[10\] constitute a consistent cognitive perspective.</Paragraph>
    <Paragraph position="5"> Any natural language understanding system must incorporate mechanisms to perform word sense dlsa?biguatlo~ in. the context .of ape, n-ended world gnow~eoge, rne Importance at these mechanisms tar wore usage diagnosis derives from the ubiquity of local ambiguities, and brought about the notion chat ~hey be made the central processes of computational analysls an 9 understanding, Consideration of almost any Engllsn content word leads to a realization of the scope of the problem -- with a little time and perhaps help from the dlctlonaFy , man~.dlstinct usages can ee.id~ntifl~d. As.a stmpie lllustrarzon, several usages earn tar the worus &amp;quot;heavy&amp;quot; and &amp;quot;ice&amp;quot; appear in Figure I. Each of. these seemingly&amp;quot; benign words exhibits a rich depth of contextual use, An earlier paper contains.a list at almost sixty verbal usages for the word &amp;quot;take&amp;quot; \[llJ. The representation of all contextual word usages in an active way t~at insures their utility for linguistic dlagnasis led to the notion of word experts. Each word expert is a procedural entit~~f all posslblq contextual interpretations of the -word it represents. = Whe~ placed in a context formed by.expqrts for thg.othe ~ wares In a sentence, earn expert ShOUld De capaole or sufficient context-problng and self-examination to determine successfully' its functional or semantic role, and further, to realize the nature of that function or the precise meaning of the word. The representation and control issues involved in basing a parser on word experts are discussed below, following presentation of an example execution of the existing Word Expert Parser.</Paragraph>
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