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## Details

Document Type: | Book |
---|---|

All Authors / Contributors: |
Frederick Jelinek; John D Lafferty; R L Mercer |

OCLC Number: | 24366955 |

Notes: | "12/13/90"--Cover. |

Description: | 116 pages : illustrations ; 28 cm. |

Series Title: | International Business Machines Corporation.; Research Division.; Research Report |

Responsibility: | by F. Jelinek, J.D. Lafferty, and R.L. Mercer. |

### Abstract:

Abstract: "The purpose of this tutorial article is to introduce methods related to probabilistic context free grammars (PCFG's), that is grammars whose production rules have attached to them a probability of being used. PCFG's have at least three advantages: (1) In an ambiguous, but appropriately specified PCFG, correct parses are high probability parses; (2) Parsing can be considerably speeded up by early pruning of low probability parses; (3) A rigorous comparison along information theoretic lines is possible of the relative qualities of rival probabilistic grammars.

We introduce four classes of algorithms that handle PCFGs: (1) Computation of the total probability that a PCFG generates a given sentence; (2) Method of finding the most probable parse tree of a given sentence; (3) Estimation of probabilities of rewriting rules of a PCFG on the basis of a text corpus; (4) Computation of the probability that the PCFG produces a sentence having a given initial substring."

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