Technical Reports (CIS)

Document Type

Technical Report

Date of this Version

June 1988

Comments

University of Pennsylvania Department of Computer and Information Science Technical Report No. MS-CIS-88-56.

Abstract

Control grammars, a generalization of context-free grammars recently introduced for use in natural language recognition, are investigated. In particular, it is shown that a hierarchy of non-context-free languages, called the Control Language Hierarchy (CLH), generated by control grammars can be recognized in polynomial time. Previously, the best known upper bound was exponential time. It is also shown that CLH is in NC(2) the class of languages recognizable by uniform boolean circuits of polynomial size and O(log2 n) depth.

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Date Posted: 31 October 2007