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<Paper uid="P04-1071">
  <Title>Wrapping of Trees</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Tree-Adjoining Grammar (TAG) (Joshi and Schabes, 1997; Joshi et al., 1975) is a grammar formalism which comes with a well-developed theory of natural language syntax (Frank, 2002; Frank, 1992; Kroch and Joshi, 1985). There are, however, a number of constructions, many in the core of language, which present difficulties for the linguistic underpinnings of TAG systems, although not necessarily for the implemented systems themselves. Most of these involve the combining of trees in ways that are more complicated than the simple embedding provided by the tree-adjunction operation.</Paragraph>
    <Paragraph position="1"> The most widely studied way of addressing these constructions within TAG-based linguistic theory (Kroch and Joshi, 1987; Kroch, 1989; Frank, 2002) has been to assume some sort of multi-component adjoining (MCTAG (Weir, 1988)), in which elementary structures are factored into sets of trees that are adjoined simultaneously at multiple points. Depending on the restrictions placed on where this adjoining can occur the effect of such extensions range from no increase in complexity of either the licensed tree sets or the computational complexity of parsing, to substantial increases in both. In this paper we explore these issues within the framework of an extension of TAG that is conservative in the sense that it preserves the unitary nature of the elementary structures and of the adjunction operation and extends the descriptive power minimally.</Paragraph>
    <Paragraph position="2"> While the paper is organized around particular syntactic phenomena, it is not a study of syntax itself. We make no attempt to provide a comprehensive theory of syntax. In fact, we attempt to simply instantiate the foundations of existing theory (Frank, 2002) in as faithful a way as possible.</Paragraph>
    <Paragraph position="3"> Our primary focus is the interplay between the linguistic theory and the formal language theory. All of the phenomena we consider can be (and in practice are (Group, 1998)) handled ad hoc with feature-structure based TAG (FTAG, (Vijay-Shanker and Joshi, 1991)). From a practical perspective, the role of the underlying linguistic theory is, at least in part, to insure consistent and comprehensive implementation of ad hoc mechanisms. From a theoretical perspective, the role of the formal language framework is, at least in part, to insure coherent and computationally well-grounded theories. Our over-all goal is to find formal systems that are as close as possible to being a direct embodiment of the principles guiding the linguistic theory and which are maximally constrained in their formal and computational complexity.</Paragraph>
  </Section>
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