1995 TheProblOfCompTheMostProbTreeInDOPParsing

(Bod, 1995) ⇒ Rens Bod. (1995). “The Problem of Computing the Most Probable Tree in Data-Oriented Parsing and Stochastic Tree Grammars.” In: Proceedings of the seventh conference on European chapter of the Association for Computational Linguistics (EACL 1995). doi:10.3115/976973.976989

Subject Headings: Syntactic Parser, Data Oriented Parsing.

Notes

Cited By

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Quotes

Abstract

We deal with the question as to whether there exists a polynomial time algorithm for computing the most probable parse tree of a sentence generated by a data-oriented parsing (DOP) model. (Scha, 1990; Bod, 1992, 1993a). Therefore we describe DOP as a stochastic tree-substitution grammar (STSG). In STSG, a tree can be generated by exponentially many derivations involving different elementary trees. The probability of a tree is equal to the sum of the probabilities of all its derivations.

We show that in STSG, in contrast with stochastic context-free grammar, the Viterbi algorithm cannot be used for computing a most probable tree of a string. We propose a simple modification of Viterbi which allows by means of a "select-random" search to estimate the most probable tree of a string in polynomial time.

Experiments with DOP on ATIS show that only in 68% of the cases, the most probable derivation of a string generates the most probable tree of that string. Therefore, the parse accuracy obtained by the most probable trees (96%) is dramatically higher than the parse accuracy obtained by the most probable derivations (65%).

It is still an open question whether the most probable tree of a string can be deterministically computed in polynomial time.

References

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	Author	volume	Date Value	title	type	journal	titleUrl	doi	note	year
1995 TheProblOfCompTheMostProbTreeInDOPParsing	Rens Bod			The Problem of Computing the Most Probable Tree in Data-Oriented Parsing and Stochastic Tree Grammars			http://acl.ldc.upenn.edu/E/E95/E95-1015.pdf