From: AAAI-91 Proceedings. Copyright ©1991, AAAI (www.aaai.org). All rights reserved. Organization of the American Association for Articial Intelligence 1991 National Conference on Articial Intelligence Program Cochairs Steve Hanks, University of Washington Thomas L. Dean, Brown University Barbara Hayes-Roth, Stanford University Kathleen McKeown, Columbia University James Hendler, University of Maryland Donald Hindle, AT&T Bell Laboratories Associate Chairs Graeme Hirst, University of Rochester Yumi Iwasaki, Stanford University Andrea P. Danyluk, Columbia University Paul Jacobs, GE Research and Development Ctr Sarah Rebecca Thomas, Stanford University Leo Joskowicz, IBM Leslie Kaelbling, Teleos Research Invited Speaker Chair Avi Kak, Purdue University Ray Perrault, SRI International Henry Kautz, AT&T Bell Laboratories Michael Kearns, ICSI Program Committee Rich Keller, NASA Ames Research Center Sanjaya Addanki, IBM John Kender, Columbia University Alice Agogino, University of California, Berkeley Richard Kittredge, University of Montreal Kevin Ashley, University of Pittsburgh Kurt Konolige, SRI International Fahiem Bacchus, University of Waterloo Richard Korf, University of California, Los Angeles Lawrence Birnbaum, Northwestern University Vipin Kumar, University of Minnesota Ruud Bolle, IBM Pat Langley, NASA Ames Research Center Wray Buntine, NASA Ames Research Center Wendy Lehnert, University of Massachusetts Tom Bylander, Ohio State University Bill Mark, Lockheed Palo Alto Research Labs Gregg Collins, Northwestern University Charles Martin, University of Chicago Johan de Kleer, Xerox PARC David McAllester, MIT AI Lab Rina Dechter, University of California, Irvine Drew Vincent McDermott, Yale University Charles Dolan, Hughes Research Lab Steve Minton, NASA Ames Research Center Edmund Durfee, University of Michigan Leora Morgenstern, IBM Corporation Charles Elkan, University of California, San Diego Paul Morris, IntelliCorp Tom Ellman, Rutgers University Jack Mostow, Rutgers University Lee Erman, Cimex Teknowledge Corp Robert Nado, Price Waterhouse Technology Centre David Etherington, AT&T Bell Laboratories Dana Nau, University of Maryland Brian Falkenhainer, Xerox PARC Terry Nutter, Virginia Tech Steve Feiner, Columbia University Becky Passoneau, Columbia University Gerhard Fischer, University of Colorado, Boulder Ramesh Patil, USC/ISI Doug Fisher, Vanderbilt University Judea Pearl, University of California, Los Angeles Eugene Freuder, University of New Hampshire Ed Pednault, AT&T Bell Laboratories Alan Frisch, University of Illinois Don Perlis, University of Maryland Les Gasser, USC Peter Pirolli, University of California, Berkeley Hector Gener, IBM Corporation Martha Pollack, SRI International Matthew Ginsberg, Stanford University Robin Popplestone, University of Massachusetts John Grefenstette, Naval Research Lab Bruce Porter, University of Texas at Austin Benjamin Grosof, IBM T. J. Watson Research Center Larry Rendell, University of Illinois at Urbana- Kristian Hammond, University of Chicago Champaign Walter Hamscher, Price Waterhouse Technology Ctr Chuck Rich, MIT AI Lab Paul Rosenbloom, USC/ISI Councilors (through 1991) Je Rosenschein, Hebrew University Elaine Rich, MCC Je Schlimmer, Carnegie Mellon University Georey Hinton, University of Toronto Len Schubert, University of Rochester Wendy Lehnert, University of Massachusetts Glenn Shafer, University of Kansas Reid Smith, Schlumberger Jude Shavlik, University of Wisconsin-Madison Yoav Shoham, Stanford University Councilors (through 1992) Howard Shrobe, Symbolics/MIT Kenneth D. Forbus, University of Illinois Reid Simmons, Carnegie Mellon University Howard Shrobe, Symbolics/MIT David Smith, Rockwell International William Swartout, USC-ISI Lynn Andrea Stein, MIT AI Lab J. Martin Tenenbaum, Stanford University Mark Stickel, SRI International Councilors (through 1993) Devika Subramanian, Cornell University Richard Sutton, GTE Laboratories Mark Fox, Carnegie Mellon University Barbara Hayes-Roth, Stanford University Bill Swartout, USC/ISI Thomas Dietterich, Oregon State University Chuck Thorpe, Carnegie Mellon University Richard Fikes, Stanford University Je Van Baalen, Price Waterhouse Technology Centre Kurt vanLehn, University of Pittsburgh Standing Committees Marc Vilain, MITRE Corporation Conference Chair: Richard Waters, MIT AI Lab Howard Shrobe, Symbolics/MIT Dan Weld, University of Washington Michael Wellman, Wright-Patterson Air Force Base Conference Cochair: Brian Williams, Xerox PARC William Swartout, USC/ISI Beverly Woolf, University of Massachusetts Finance Chair: Bruce Buchanan, University of Pittsburgh Auxiliary Reviewers Publications Chair: Mark Fox, Carnegie Mellon University G. Y. Ananth, University of Minnesota Scholarship Chair: Mark Boddy, Brown University Barbara Hayes-Roth, Stanford University Norman Dalkey, University of California, Los Angeles Yolanda Gil, Carnegie Mellon University Symposium Chair: Peter Patel-Schneider, AT&T Bell Laboratories Robert P. Goldman, Tulane University Moises Goldszmidt, University of California, Los An- Symposium Cochairs: geles James Hendler, University of Maryland Diane F. Gordon, Naval Research Lab Wendy Lehnert, University of Massachusetts Adam Grove, Stanford University Workshop Grants: Robert Holte, University of Ottawa Kathy McKeown, Columbia University Scott Hunter, Cornell University AI in Medicine Subgroup Liaison: Keiji Kanazawa, Brown University Gordon Banks, University of Pittsburgh Itay Meiri, University of California, Los Angeles AI in Manufacturing Subgroup Liaison: S. Shekhar, University of Minnesota Karl Kempf, Intel J. Srivastava, University of Minnesota AI and the Law Subgroup Liaison: Fangzhen Lin, Stanford University Edwina Rissland, University of Massachusetts Thomas Verma, University of California, Los Angeles AI and Business Subgroup Liaison: Dan O’Leary, University of Southern California AAAI Ocials AAAI Sta President: Executive Director: Claudia Mazzetti Daniel G. Bobrow, Xerox Palo Alto Research Center Managing Director: Carol McKenna Hamilton President-elect: Accountant: Julie G.Bowen Patrick Hayes, MCC CYC-West Membership & Systems Coordinator: Richard A. Skalsky Past President: Conference Coordinator: Annette Eldredge Raj Reddy, Carnegie Mellon University Conference Coordinator: Mary Livingston Secretary-Treasurer: Administrative: Hasina Aziz, Daphne Black, Arthur Bruce Buchanan, University of Pittsburgh Okorie, and Godwin Okorie AI Magazine Sta The AAAI Press Editor-in-Chief: The MIT Press Coliaisons: Robert Engelmore, Stanford University Robert Prior and Teresa Ehling, The MIT Press Associate Editor: Editor-in-Chief: Elaine Rich, MCC William Clancey, Institute for Research on Learning Associate Editor: Publishing Consultant: Ramesh Patil, USC/ISI David Mike Hamilton, The Live Oak Press Associate Editor, Book Reviews: Bruce D’Ambrosio, Oregon State University Management Board Associate Editor, Workshop Reports: William Clancey, Institute for Research on Learning Peter Patel-Schneider, AT&T Bell Labs David Mike Hamilton, The Live Oak Press Claudia Mazzetti, AAAI Associate Editor, AAAI News: Robert Prior, The MIT Press William J. 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