TAILIEUCHUNG - Báo cáo khoa học: "Bayesian Synchronous Tree-Substitution Grammar Induction and its Application to Sentence Compression"

We describe our experiments with training algorithms for tree-to-tree synchronous tree-substitution grammar (STSG) for monolingual translation tasks such as sentence compression and paraphrasing. These translation tasks are characterized by the relative ability to commit to parallel parse trees and availability of word alignments, yet the unavailability of large-scale data, calling for a Bayesian tree-to-tree formalism. | Bayesian Synchronous Tree-Substitution Grammar Induction and its Application to Sentence Compression Elif Yamangil and Stuart M. Shieber Harvard University Cambridge Massachusetts USA elif shieber @ Abstract We describe our experiments with training algorithms for tree-to-tree synchronous tree-substitution grammar STSG for monolingual translation tasks such as sentence compression and paraphrasing. These translation tasks are characterized by the relative ability to commit to parallel parse trees and availability of word alignments yet the unavailability of large-scale data calling for a Bayesian tree-to-tree formalism. We formalize nonparametric Bayesian STSG with epsilon alignment in full generality and provide a Gibbs sampling algorithm for posterior inference tailored to the task of extractive sentence compression. We achieve improvements against a number of baselines including expectation maximization and variational Bayes training illustrating the merits of nonparametric inference over the space of grammars as opposed to sparse parametric inference with a fixed grammar. 1 Introduction Given an aligned corpus of tree pairs we might want to learn a mapping between the paired trees. Such induction of tree mappings has application in a variety of natural-language-processing tasks including machine translation paraphrase and sentence compression. The induced tree mappings can be expressed by synchronous grammars. Where the tree pairs are isomorphic synchronous context-free grammars SCFG may suffice but in general non-isomorphism can make the problem of rule extraction difficult Galley and McKeown 2007 . More expressive formalisms such as syn chronous tree-substitution Eisner 2003 or treeadjoining grammars may better capture the pairings. In this work we explore techniques for inducing synchronous tree-substitution grammars STSG using as a testbed application extractive sentence compression. Learning an STSG from aligned trees is tantamount to .

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