1. T. Berners-Lee and D. J. Weitzner are at the Computer Science and Artificial Intelligence Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
2. W. Hall and N. Shadbolt are in the School of Electronics and Computer Science, University of Southampton, Southampton SO17 1BJ, UK.
3. J. Hendler is in the Computer Science Department, University of Maryland, College Park, MD 20742, USA.