tailieunhanh - Báo cáo khoa học: "Pipeline Iteration"

This paper presents pipeline iteration, an approach that uses output from later stages of a pipeline to constrain earlier stages of the same pipeline. We demonstrate significant improvements in a state-of-the-art PCFG parsing pipeline using base-phrase constraints, derived either from later stages of the parsing pipeline or from a finitestate shallow parser. The best performance is achieved by reranking the union of unconstrained parses and relatively heavilyconstrained parses. | Pipeline Iteration Kristy Hollingshead and Brian Roark Center for Spoken Language Understanding OGI School of Science Engineering Oregon Health Science University Beaverton Oregon 97006 USA hollingk roark @ Abstract This paper presents pipeline iteration an approach that uses output from later stages of a pipeline to constrain earlier stages of the same pipeline. We demonstrate significant improvements in a state-of-the-art PCFG parsing pipeline using base-phrase constraints derived either from later stages of the parsing pipeline or from a finite-state shallow parser. The best performance is achieved by reranking the union of unconstrained parses and relatively heavily-constrained parses. 1 Introduction A pipeline system consists of a sequence of processing stages such that the output from one stage provides the input to the next. Each stage in such a pipeline identifies a subset of the possible solutions and later stages are constrained to find solutions within that subset. For example a part-of-speech tagger could constrain a base phrase chunker Rat-naparkhi 1999 or the n-best output of a parser could constrain a reranker Charniak and Johnson 2005 . A pipeline is typically used to reduce search complexity for rich models used in later stages usually at the risk that the best solutions may be pruned in early stages. Pipeline systems are ubiquitous in natural language processing used not only in parsing Rat-naparkhi 1999 Charniak 2000 but also machine translation Och and Ney 2003 and speech recognition Fiscus 1997 Goel et al. 2000 among others. Despite the widespread use of pipelines they have been understudied with very little work on general techniques for designing and improving pipeline systems although cf. Finkel et al. 2006 . This paper presents one such general technique here applied to stochastic parsing whereby output from 952 later stages of a pipeline is used to constrain earlier stages of the same pipeline. To our knowledge this is the .