TAILIEUCHUNG - Báo cáo khoa học: "Boosting-based parse reranking with subtree features"

This paper introduces a new application of boosting for parse reranking. Several parsers have been proposed that utilize the all-subtrees representation (., tree kernel and data oriented parsing). This paper argues that such an all-subtrees representation is extremely redundant and a comparable accuracy can be achieved using just a small set of subtrees. We show how the boosting algorithm can be applied to the all-subtrees representation and how it selects a small and relevant feature set efficiently. Two experiments on parse reranking show that our method achieves comparable or even better performance than kernel methods and also improves the. | Boosting-based parse reranking with subtree features Taku Kudo Jun Suzuki Hideki Isozaki NTT Communication Science Laboratories. 2-4 Hikaridai Seika-cho Soraku Kyoto Japan taku jun isozaki @ Abstract This paper introduces a new application of boosting for parse reranking. Several parsers have been proposed that utilize the all-subtrees representation . tree kernel and data oriented parsing . This paper argues that such an all-subtrees representation is extremely redundant and a comparable accuracy can be achieved using just a small set of subtrees. We show how the boosting algorithm can be applied to the all-subtrees representation and how it selects a small and relevant feature set efficiently. Two experiments on parse reranking show that our method achieves comparable or even better performance than kernel methods and also improves the testing efficiency. 1 Introduction Recent work on statistical natural language parsing and tagging has explored discriminative techniques. One of the novel discriminative approaches is reranking where discriminative machine learning algorithms are used to rerank the n-best outputs of generative or conditional parsers. The discriminative reranking methods allow us to incorporate various kinds of features to distinguish the correct parse tree from all other candidates. With such feature design flexibility it is nontrivial to employ an appropriate feature set that has a good discriminative ability for parse reranking. In early studies feature sets were given heuristically by simply preparing task-dependent feature templates Collins 2000 Collins 2002 . These ad-hoc solutions might provide us with reasonable levels of per Currently Google Japan Inc. taku@ formance. However they are highly task dependent and require careful design to create the optimal feature set for each task. Kernel methods offer an elegant solution to these problems. They can work on a potentially huge or even infinite number of .

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