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<Paper uid="C04-1028">
  <Title>Generalizing Dimensionality in Combinatory Categorial Grammar</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> The information conveyed by linguistic utterances is diverse, detailed, and complex. To properly analyze what is communicated by an utterance, this information must be encoded and interpreted at many levels. The literature contains various proposals for dealing with many of these levels in the description of natural language grammar.</Paragraph>
    <Paragraph position="1"> Since information flows between different levels of analysis, it is common for linguistic formalisms to bundle them together and provide some means for communication between them. Categorial grammars, for example, normally employ a Saussurian sign that relates a surface string with its syntactic category and the meaning it expresses. Syntactic analysis is entirely driven by the categories, and when information from other levels is used to affect the derivational possibilities, it is typically loaded as extra information on the categories.</Paragraph>
    <Paragraph position="2"> Head-driven Phrase Structure Grammar (HPSG) (Pollard and Sag, 1993) and Lexical Functional Grammar (LFG) (Kaplan and Bresnan, 1982) also use complex signs. However, these signs are monolithic structures which permit information to be freely shared across all dimensions: any given dimension can place restrictions on another. For example, variables resolved during the construction of the logical form can block a syntactic analysis. This provides a clean, unified formal system for dealing with the different levels, but it also can adversely affect the complexity of parsing grammars written in these frameworks (Maxwell and Kaplan, 1993).</Paragraph>
    <Paragraph position="3"> We thus find two competing perspectives on communication between levels in a sign. In this paper, we propose a generalization of linguistic signs for Combinatory Categorial Grammar (CCG) (Steedman, 2000b). This generalization enables different levels of linguistic information to be represented but limits their interaction in a resource-bounded manner, following White (2004). This provides a clean separation of the levels and allows them to be designed and utilized in a more modular fashion. Most importantly, it allows us to retain the parsing complexity of CCG while gaining the representational advantages of the HPSG and LFG paradigms.</Paragraph>
    <Paragraph position="4"> To illustrate the approach, we use it to model various aspects of the realization of information structure, an inherent aspect of the (linguistic) meaning of an utterance. Speakers use information structure to present some parts of that meaning as depending on the preceding discourse context and others as affecting the context by adding new content.</Paragraph>
    <Paragraph position="5"> Languages may realize information structure using different, often interacting means, such as word order, prosody, (marked) syntactic constructions, or morphological marking (Vallduv'i and Engdahl, 1996; Kruijff, 2002). The literature presents various proposals for how information structure can be captured in categorial grammar (Steedman, 2000a; Hoffman, 1995; Kruijff, 2001). Here, we model the essential aspects of these accounts in a more perspicuous manner by using our generalized signs.</Paragraph>
    <Paragraph position="6"> The main outcomes of the proposal are threefold: (1) CCG gains a more flexible and general kind of sign; (2) these signs contain multiple levels that interact in a modular fashion and are built via CCG derivations without increasing parsing complexity; and (3) we use these signs to simplify previous CCG's accounts of the effects of word order and prosody on information structure.</Paragraph>
  </Section>
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