Methods for Obtaining corresponding Phrase Structure and Dependency Grammars

Two methods are given for converting grammars belonging to different systems. One converts a s~mple (context-free) phrase structure grammar (SPG) into a corresponding dependency grammar (DG); the other converts a DG into a corresponding SPG. The structures assigned to a string by a source grammar will correspond systematically, though asymmetrically, to those assigned by the target grammar resulting from its conversion. Since both systems are wealdy equivalent, generating exactly the CF languages , the methods facilitate experimentation with either notation in devising rules for any CF language or any CF set of strings designed to undergo subsequent transformation. A source SPG is assumed to be of'finite degree with ordered rules in which only the initial symbol is recursive. Unless the source grammars obey additional constraints, the target grammars may exhibit a peculiar property, defined as "structure sensi-tivity". The linguistic implications of the property are discussed, and the linguistic motivation for imposing the constraints necessary to avoid its appearance is suggested. The author owes an especial debt to Jesse Wright of the Automata Theory and Computability Group in the Mathematical Science Department of IBM Research for many helpful discussior~s of theoretical problems arising in the course of this investigation.