Worst-Case Synchronous Grammar Rules
نویسندگان
چکیده
We relate the problem of finding the best application of a Synchronous ContextFree Grammar (SCFG) rule during parsing to a Markov Random Field. This representation allows us to use the theory of expander graphs to show that the complexity of SCFG parsing of an input sentence of length N is Ω(N cn), for a grammar with maximum rule length n and some constant c. This improves on the previous best result of Ω(N c √ n).
منابع مشابه
Factoring Synchronous Grammars by Sorting
Synchronous Context-Free Grammars (SCFGs) have been successfully exploited as translation models in machine translation applications. When parsing with an SCFG, computational complexity grows exponentially with the length of the rules, in the worst case. In this paper we examine the problem of factorizing each rule of an input SCFG to a generatively equivalent set of rules, each having the smal...
متن کاملTwo monolingual parses are better than one (synchronous parse)
We describe a synchronous parsing algorithm that is based on two successive monolingual parses of an input sentence pair. Although the worst-case complexity of this algorithm is and must be O(n) for binary SCFGs, its average-case run-time is far better. We demonstrate that for a number of common synchronous parsing problems, the two-parse algorithm substantially outperforms alternative synchron...
متن کاملContext-Free Grammar Parsing by Message Passing
A message passing algorithm for parsing context-free grammars (CFG) is presented. The grammar is represented by a network, whose nodes represent rules and non-terminals and whose links represent the structural relationships between the rules and non-terminals. The message passing algorithm computes a shared, packed parse forest for the input sentence. The algorithm has the following characteris...
متن کاملHierarchical Back-off Modeling of Hiero Grammar based on Non-parametric Bayesian Model
In hierarchical phrase-based machine translation, a rule table is automatically learned by heuristically extracting synchronous rules from a parallel corpus. As a result, spuriously many rules are extracted which may be composed of various incorrect rules. The larger rule table incurs more disk and memory resources, and sometimes results in lower translation quality. To resolve the problems, we...
متن کاملIssues Concerning Decoding with Synchronous Context-free Grammar
We discuss some of the practical issues that arise from decoding with general synchronous context-free grammars. We examine problems caused by unary rules and we also examine how virtual nonterminals resulting from binarization can best be handled. We also investigate adding more flexibility to synchronous context-free grammars by adding glue rules and phrases.
متن کامل