Tim Griffin
University Senior Lecturer
Computer Laboratory
Cambridge University
William Gates Building
15 JJ Thomson Avenue
Cambridge - CB3 0FD - UK
E-mail: Timothy.Griffin AT cl.cam.ac.uk
Boon Thau Loo
Assistant Professor
Dept. of Computer and Infomation Science
University of Pennsylvania
605 Levine Hall,
3330 Walnut Street,
Philadelphia, PA 19104-6389, USA
E-mail: boonloo AT cis.upenn.edu