TAILIEUCHUNG - Báo cáo khoa học: "Deep Syntactic Processing by Combining Shallow Methods"

We present a novel approach for finding discontinuities that outperforms previously published results on this task. Rather than using a deeper grammar formalism, our system combines a simple unlexicalized PCFG parser with a shallow pre-processor. This pre-processor, which we call a trace tagger, does surprisingly well on detecting where discontinuities can occur without using phase structure information. | Deep Syntactic Processing by Combining Shallow Methods Peter Dienes and Amit Dubey Department of Computational Linguistics Saarland University POBox 15 11 50 66041 Saarbrucken Germany dienes adubey @ Abstract We present a novel approach for finding discontinuities that outperforms previously published results on this task. Rather than using a deeper grammar formalism our system combines a simple un-lexicalized PCFG parser with a shallow pre-processor. This pre-processor which we call a trace tagger does surprisingly well on detecting where discontinuities can occur without using phase structure information. 1 Introduction In this paper we explore a novel approach for finding long-distance dependencies. In particular we detect such dependencies or discontinuities in a two-step process i a conceptually simple shallow tagger looks for sites of discontinuties as a preprocessing step before parsing ii the parser then finds the dependent constituent antecedent . Clearly information about long-distance relationships is vital for semantic interpretation. However such constructions prove to be difficult for stochastic parsers Collins et al. 1999 and they either avoid tackling the problem Charniak 2000 Bod 2003 or only deal with a subset of the problematic cases Collins 1997 . Johnson 2002 proposes an algorithm that is able to find long-distance dependencies as a postprocessing step after parsing. Although this algorithm fares well it faces the problem that stochastic parsers not designed to capture non-local dependencies may get confused when parsing a sentence with discontinuities. However the approach presented here is not susceptible to this shortcoming as it finds discontinuties before parsing. Overall we present three primary contributions. First we extend the mechanism of adding gap variables for nodes dominating a site of discontinuity Collins 1997 . This approach allows even a context-free parser to reliably recover antecedents given prior information

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