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An important characteristic of an
FB-LTAG is that it is lexicalized, i.e., each lexical item is anchored to a
tree structure that encodes subcategorization information. Trees with the same
canonical subcategorizations are grouped into tree families. The reuse of tree
substructures, such as wh-movement,
in many different trees
creates redundancy, which poses a problem for grammar development
and maintenance [#!vijay-schabes92!#]. To consistently implement a change in
some general aspect of the design of the grammar, all the relevant trees
currently must be inspected and edited. Vijay Shanker and Schabes suggested
the use of hierarchical organization and of tree descriptions to specify
substructures that would be present in several elementary trees of a grammar.
Since then, in addition to ourselves,
Becker, [#!becker94!#], Evans et al. [#!Evans95!#], and
Candito[#!Candito96!#] have
developed systems for organizing trees of a TAG which could be used for
developing and maintaining grammars.
Our system is based
on the ideas expressed in Vijay-Shanker and Schabes, [#!vijay-schabes92!#], to
use partial-tree descriptions in specifying a grammar by separately defining
pieces of tree structures to encode independent syntactic principles. Various
individual specifications are then combined to form the elementary trees of the
grammar. The chapter begins with a description of
our grammar development system, and its implementation. We will then
show the main results of using this tool to generate
the Penn English grammar as well as a Chinese
TAG. We describe the significant properties of both grammars, pointing out the
major differences between them, and the methods by which our system is informed
about these language-specific properties. The chapter ends with the conclusion
and future work.
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Up: Lexical Organization
Previous: Lexical Organization
XTAG Project
http://www.cis.upenn.edu/~xtag