This book is based on research I did in the Stanford University Computer Science Department for the degree of Doctor of Philosophy. I express my sincere gratitude to my dissertation reading committee: Terry Winograd, Gary Hendrix, Doug Lenat and Nils Nilsson. Their discussion and comments contributed greatly to the research reported here. Barbara Grosz's thoughtful comments on my thesis contributed significantly to the quality of the research. I also thank Phil Cohen and Bonnie Webber for providing detailed comments on the first draft of this book and for providing many useful suggestions, and Aravind Joshi for his efforts in editing the Cambridge University Press Studies in Natural Language Processing series.

This research was supported by the Office of Naval Research under contract N00014-80-C-0296, and by the National Science Foundation under grant MCS-8115105. The preparation of this book was in part made possible by a gift from the System Development Foundation to SRI International as part of a coordinated research effort with the Center for the Study of Language and Information at Stanford University.

This book would be totally unreadable were it not for the efforts of SRI International Senior Technical Editor Savel Kliachko, who transformed my muddled ramblings into golden prose.