Indexed Languages and Uni cation
Grammars
y
Tore Burheim
Abstract
Indexed languages are interesting in computational linguistics b ecause they
are the least class of languages in the Chomsky hierarchy that has not b een
shown not to b e adequate to describ e the string set of natural language sen
tences We here de ne a class of uni cation grammars that exactly describ e
the class of indexed languages