tailieunhanh - Báo cáo khoa học: "Adjoining Tree-to-String Translation"

We introduce synchronous tree adjoining grammars (TAG) into tree-to-string translation, which converts a source tree to a target string. Without reconstructing TAG derivations explicitly, our rule extraction algorithm directly learns tree-to-string rules from aligned Treebank-style trees. As tree-to-string translation casts decoding as a tree parsing problem rather than parsing, the decoder still runs fast when adjoining is included. | Adjoining Tree-to-String Translation Yang Liu Qun Liu and Yajuan Lii Key Laboratory of Intelligent Information Processing Institute of Computing Technology Chinese Academy of Sciences . Box 2704 Beijing 100190 China yliu liuqun lvyajuan @ Abstract We introduce synchronous tree adjoining grammars TAG into tree-to-string translation which converts a source tree to a target string. Without reconstructing TAG derivations explicitly our rule extraction algorithm directly learns tree-to-string rules from aligned Treebank-style trees. As tree-to-string translation casts decoding as a tree parsing problem rather than parsing the decoder still runs fast when adjoining is included. Less than 2 times slower the adjoining tree-to-string system improves translation quality by BLEU over the baseline system only allowing for tree substitution on NIST Chinese-English test sets. 1 Introduction Syntax-based translation models which exploit hierarchical structures of natural languages to guide machine translation have become increasingly popular in recent years. So far most of them have been based on synchronous context-free grammars CFG Chiang 2007 tree substitution grammars TSG Eisner 2003 Galley et al. 2006 Liu et al. 2006 Huang et al. 2006 Zhang et al. 2008 and inversion transduction grammars ITG Wu 1997 Xiong et al. 2006 . Although these formalisms present simple and precise mechanisms for describing the basic recursive structure of sentences they are not powerful enough to model some important features of natural language syntax. For example Chiang 2006 points out that the translation of languages that can stack an unbounded number of clauses in an inside-out way Wu 1997 1278 provably goes beyond the expressive power of synchronous CFG and TSG. Therefore it is necessary to find ways to take advantage of more powerful synchronous grammars to improve machine translation. Synchronous tree adjoining grammars TAG Shieber and Schabes 1990 are a good candidate. As a .

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