TAILIEUCHUNG - Báo cáo khoa học: "Efficient Third-order Dependency Parsers"

We present algorithms for higher-order dependency parsing that are “third-order” in the sense that they can evaluate substructures containing three dependencies, and “efficient” in the sense that they require only O(n4 ) time. Importantly, our new parsers can utilize both sibling-style and grandchild-style interactions. We evaluate our parsers on the Penn Treebank and Prague Dependency Treebank, achieving unlabeled attachment scores of and , respectively. | Efficient Third-order Dependency Parsers Terry Koo and Michael Collins MIT CSAIL Cambridge MA 02139 USA maestro mcollins @ Abstract We present algorithms for higher-order dependency parsing that are third-order in the sense that they can evaluate substructures containing three dependencies and efficient in the sense that they require only O n4 time. Importantly our new parsers can utilize both sibling-style and grandchild-style interactions. We evaluate our parsers on the Penn Treebank and Prague Dependency Treebank achieving unlabeled attachment scores of and respectively. 1 Introduction Dependency grammar has proven to be a very useful syntactic formalism due in no small part to the development of efficient parsing algorithms Eisner 2000 McDonald et al. 2005b McDonald and Pereira 2006 Carreras 2007 which can be leveraged for a wide variety of learning methods such as feature-rich discriminative models Lafferty et al. 2001 Collins 2002 Taskar et al. 2003 . These parsing algorithms share an important characteristic they factor dependency trees into sets of parts that have limited interactions. By exploiting the additional constraints arising from the factorization maximizations or summations over the set of possible dependency trees can be performed efficiently and exactly. A crucial limitation of factored parsing algorithms is that the associated parts are typically quite small losing much of the contextual information within the dependency tree. For the purposes of improving parsing performance it is desirable to increase the size and variety of the parts used by the At the same time the need for more expressive factorizations 1For examples of how performance varies with the degree of the parser s factorization see . McDonald and Pereira 2006 Tables 1 and 2 Carreras 2007 Table 2 Koo et al. 2008 Tables 2 and 4 or Suzuki et al. 2009 Tables 3-6 . must be balanced against any resulting increase in the computational cost of

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