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<Paper uid="E91-1043">
  <Title>A LANGUAGE i BIDIRECTIONAL MODEL FOR NATURAL PROCESSING</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
PROBLEMS OF BIDIRECTIONAL
GRAMMATICAL PROCESSING
</SectionTitle>
    <Paragraph position="0"> use different knowledge sources that are compiled from the same source (e.g., Horacek and Pyka 1988) and systems that use common basic representation devices * (e.g., Lancel et,al. 1988; Neumann and Finkler 1990).</Paragraph>
    <Paragraph position="1"> - 245 Currently developed approaches that consider parsing as well as generation (e.g., Shieber 1988; Shieber et al. 1990; Dymetman et al. 1990; van Noord 1990; Zajac and Emele 1990) assume: deg that both tasks take place independently from each other, i.e. an utterance is either generated or parsed and * that grammatical processing can be performed without considerations of discourse.</Paragraph>
    <Paragraph position="2"> A great problem with this view is that it offers no solution of the problem of choice between paraphrases in generation: The proposed approaches assume - more or less explicitly modularity between the conceptual and grammatical component of a natural language system. 2 A great advantage of a modular design especially for uniform architectures is that it is possible to view the grammatical component as relatively autonomous and self-contained (cf. Appelt 87).</Paragraph>
    <Paragraph position="3"> But then the following problems emerge: The conceptual component will be unable to exactly specify the logical form as input to the grammatical component that will precisely lead to the utterance that reflects the intended meaning unless the conceptual module has detailed information about the grammar and knows when to use a specific construction (which renders the modular design meaningless).</Paragraph>
    <Paragraph position="4"> On the other hand, when parsing and generation are performed within the grammatical component by a single process only then the opposite view of computing all possible parses of an utterance is the computation of all possible paraphrases of a logical form. When gramm~ttical processing should be modelled by means of a bidirectional grammar, the declarative structure of the grammar must not contain pragmatical or stylistical information because of the modular design. But then the process can only choose randomly between paraphrases during generation and this means that the intended meaning will possibly not be conveyed.</Paragraph>
    <Paragraph position="5"> Ideally, a logical language would be helpful which necessarily and sufficiently represents all meaning distinctions of natural 2By a conceptual component I mean either the what-to-say component of a generation system or the component that performs inference, plan recognition or anaphora resolution of an understanding system. language. But as Shieber (1988) states &amp;quot;this ... is just the central problem of knowledge representation for natural language 10 general&amp;quot;. Currently, there exist only approximate solutions to this problem for example the use of canonical logical forms (cf. Shieber 88). 3 But this still offers no solution of the problem of choice between paraphrases.</Paragraph>
    <Paragraph position="6"> In this paper it will be argued that the following two points will contribute to an approximate solution: * interleaved parsing and generation deg using the language use of interlocutors as an additional access criterion to linguistic knowledge Interleaved parsing and generation means that both tasks take place in parallel (see section 2). In principle this results in a bidirectional and incremental flow of information during natural language processing (see section 4.1). An important point during the use of language is that the Choice of linguistic material is influenced by the language use of others (see section 3). This leads to more flexibility: not all necessary parameters (e.g., pragmatical values) need to be specified in the input of a generator because decision points can also be set dynamically during run-time.</Paragraph>
    <Paragraph position="7"> A promising approach to realize these two features will be to base grammatical processing on a uniform process that is parametrized by means of a declaratively specified preference structure of knowledge sources. But, it is necessary to be aware that the grammatical component must be assumed to be an integrated part of a whole natural language system (in particular in models for performing dialogs) in order to realize this solution. ; Before the architecture of the model will be described in section 4 the two issues are explained in more detail in the next sections.</Paragraph>
  </Section>
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