[1] IIT, Dept Comp Sci, Concurrent Programming Res Grp, Chicago, IL 60616 USA
[2] Univ Twente, Dept Comp Sci, Enschede, Netherlands
[3] Univ British Columbia, Sierra Syst Chair Software Design, Xerox, Vancouver, BC V5Z 1M9, Canada
[4] Xerox PARC, Palo Alto, CA USA
[5] Northeastern Univ, Boston, MA 02115 USA