M. Tamer �zsu is a professor of computer science at the University of Waterloo, Canada. He has been conducting research in distributed data management for thirty years. He serves on the editorial boards of many journals and book series, and is also the co-editor-in-chief, with Ling Liu, of the Encyclopedia of Database Systems. Patrick Valduriez is a senior researcher at INRIA, France and the head of the Zenith research group pursuing research in scientific data management in distributed systems. He has also served as a professor of computer science at University Paris 6. He has authored and co-authored over 200 technical papers and several books.