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Báo cáo khoa học: "Parsing with generative models of predicate-argument structure"

The model used by the CCG parser of Hockenmaier and Steedman (2002b) would fail to capture the correct bilexical dependencies in a language with freer word order, such as Dutch. This paper argues that probabilistic parsers should therefore model the dependencies in the predicate-argument structure, as in the model of Clark et al. (2002), and defines a generative model for CCG derivations that captures these dependencies, including bounded and unbounded long-range dependencies. | Parsing with generative models of predicate-argument structure Julia Hockenmaier IRCS University of Pennsylvania Philadelphia USA and Informatics University of Edinburgh Edinburgh UK juliahr@linc.cis.upenn.edu Abstract The model used by the CCG parser of Hockenmaier and Steedman 2002b would fail to capture the correct bilexical dependencies in a language with freer word order such as Dutch. This paper argues that probabilistic parsers should therefore model the dependencies in the predicate-argument structure as in the model of Clark et al. 2002 and defines a generative model for CCG derivations that captures these dependencies including bounded and unbounded long-range dependencies. 1 Introduction State-of-the-art statistical parsers for Penn Treebank-style phrase-structure grammars Collins 1999 Charniak 2000 but also for Categorial Grammar Hockenmaier and Steedman 2002b include models of bilexical dependencies defined in terms of local trees. However this paper demonstrates that such models would be inadequate for languages with freer word order. We use the example of Dutch ditransitives but our argument equally applies to other languages such as Czech see Collins et al. 1999 . We argue that this problem can be avoided if instead the bilexical dependencies in the predicate-argument structure are captured and propose a generative model for these dependencies. The focus of this paper is on models for Combinatory Categorial Grammar CCG Steedman 2000 . Due to CCG s transparent syntax-semantics interface. the parser has direct and immediate access to the predicate-argument structure which includes not only local but also long-range dependencies arising through coordination extraction and control. These dependencies can be captured by our model in a sound manner and our experimental results for English demonstrate that their inclusion improves parsing performance. However since the predicate-argument structure itself depends only to a degree on the grammar formalism it