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Computational Linguistics

Hwee Tou Ng, Editor
March 2009, Vol. 35, No. 1, Pages 47-59
(doi: 10.1162/coli.07-031-R2-06-98)
© 2009 Association for Computational Linguistics
The Complexity of Ranking Hypotheses in Optimality Theory
Article PDF (137.81 KB)

Given a constraint set with k constraints in the framework of Optimality Theory (OT), what is its capacity as a classification scheme for linguistic data? One useful measure of this capacity is the size of the largest data set of which each subset is consistent with a different grammar hypothesis. This measure is known as the Vapnik-Chervonenkis dimension (VCD) and is a standard complexity measure for concept classes in computational learnability theory. In this work, I use the three-valued logic of Elementary Ranking Conditions to show that the VCD of Optimality Theory with k constraints is k-1. Analysis of OT in terms of the VCD establishes that the complexity of OT is a well-behaved function of k and that the ‘hardness’ of learning in OT is linear in k for a variety of frameworks that employ probabilistic definitions of learnability.