BLEU: a method for automatic evaluation of machine translation
ACL '02 Proceedings of the 40th Annual Meeting on Association for Computational Linguistics
Synchronous binarization for machine translation
HLT-NAACL '06 Proceedings of the main conference on Human Language Technology Conference of the North American Chapter of the Association of Computational Linguistics
Hierarchical Phrase-Based Translation
Computational Linguistics
Efficient parsing for transducer grammars
NAACL '09 Proceedings of Human Language Technologies: The 2009 Annual Conference of the North American Chapter of the Association for Computational Linguistics
Cube pruning as heuristic search
EMNLP '09 Proceedings of the 2009 Conference on Empirical Methods in Natural Language Processing: Volume 1 - Volume 1
Prefix probability for probabilistic synchronous context-free grammars
HLT '11 Proceedings of the 49th Annual Meeting of the Association for Computational Linguistics: Human Language Technologies - Volume 1
Terminal-aware synchronous binarization
HLT '11 Proceedings of the 49th Annual Meeting of the Association for Computational Linguistics: Human Language Technologies: short papers - Volume 2
Issues concerning decoding with synchronous context-free grammar
HLT '11 Proceedings of the 49th Annual Meeting of the Association for Computational Linguistics: Human Language Technologies: short papers - Volume 2
Agreement constraints for statistical machine translation into German
WMT '11 Proceedings of the Sixth Workshop on Statistical Machine Translation
Augmenting string-to-tree translation models with fuzzy use of source-side syntax
EMNLP '11 Proceedings of the Conference on Empirical Methods in Natural Language Processing
NAACL HLT '12 Proceedings of the 2012 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies
GHKM rule extraction and scope-3 parsing in Moses
WMT '12 Proceedings of the Seventh Workshop on Statistical Machine Translation
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Conventional wisdom dictates that synchronous context-free grammars (SCFGs) must be converted to Chomsky Normal Form (CNF) to ensure cubic time decoding. For arbitrary SCFGs, this is typically accomplished via the synchronous binarization technique of (Zhang et al., 2006). A drawback to this approach is that it inflates the constant factors associated with decoding, and thus the practical running time. (DeNero et al., 2009) tackle this problem by defining a superset of CNF called Lexical Normal Form (LNF), which also supports cubic time decoding under certain implicit assumptions. In this paper, we make these assumptions explicit, and in doing so, show that LNF can be further expanded to a broader class of grammars (called "scope-3") that also supports cubic-time decoding. By simply pruning non-scope-3 rules from a GHKM-extracted grammar, we obtain better translation performance than synchronous binarization.