tailieunhanh - Báo cáo khoa học: "Parse Forest Computation of Expected Governors"

In a headed tree, each terminal word can be uniquely labeled with a governing word and grammatical relation. This labeling is a summary of a syntactic analysis which eliminates detail, reflects aspects of semantics, and for some grammatical relations (such as subject of finite verb) is nearly uncontroversial. We define a notion of expected governor markup, which sums vectors indexed by governors and scaled by probabilistic tree weights. The quantity is computed in a parse forest representation of the set of tree analyses for a given sentence, using vector sums and scaling by inside probability and flow. . | Parse Forest Computation of Expected Governors Helmut Schmid Institute for Computational Linguistics University of Stuttgart Azenbergstr. 12 70174 Stuttgart Germany schmid@ Mats Rooth Department of Linguistics Cornell University Morrill Hall Ithaca NY 14853 USA mats@ Abstract In a headed tree each terminal word can be uniquely labeled with a governing word and grammatical relation. This labeling is a summary of a syntactic analysis which eliminates detail reflects aspects of semantics and for some grammatical relations such as subject of finite verb is nearly un-controversial. We define a notion of expected governor markup which sums vectors indexed by governors and scaled by probabilistic tree weights. The quantity is computed in a parse forest representation of the set of tree analyses for a given sentence using vector sums and scaling by inside probability and flow. 1 Introduction A labeled headed tree is one in which each nonterminal vertex has a distinguished head child and in the usual way non-terminal nodes are labeled with non-terminal symbols syntactic categories such as NP and terminal vertices are labeled with terminal symbols words such as The governor algorithm was designed and implemented in the Reading Comprehension research group in the 2000 Workshop on Language Engineering at Johns Hopkins University. Thanks to Marc Light Ellen Riloff Pranav Anand Brianne Brown Eric Breck Gideon Mann and Mike Thelen for discussion and assistance. Oral presentations were made at that workshop in August 2000 and at the University of Sussex in January 2001. Thanks to Fred Jelinek John Carroll and other members of the audiences for their comments. NPpeter I Peter read reads Sead VPr NP . . 1511paper PP onmarkup P onố NP- . L. 1511paper Vevery Npaper r ÍL every paper NProartep I Nmarfcizp I markup on Figure 1 A tree with percolated lexical heads. reads 1 We work with syntactic trees in which terminals are in addition labeled with .

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