| Deborah L. McGuinness dlm@research.att.com Merryll K. Abrahams Lori Alperin Resnick resnick@research.att.com AT&T Labs - Research Florham Park, NJ | Peter F. Patel-Schneider pfps@research.bell-labs..com Bell Labs Research 600 Mountain Avenue Murray Hill, NJ 07974 | Richmond H. Thomason thomason@Pogo.isp.pitt.edu Violetta Cavalli-Sforza Cristina Conati Intelligent Systems Program University of Pittsburgh Pittsburgh, PA 15260 |