Department of Computer Science, University of California, Santa Cruz, Santa Cruz, CA 95064, USA. booch@cse.usc.edu|Department of Computer Science, University of California, Santa Cruz, Santa Cruz, CA 95064, USA. booch@cse.usc.edu|Department of Computer Science, University of California, Santa Cruz, Santa Cruz, CA 95064, USA. booch@cse.usc.edu|Department of Computer Science, University of California, Santa Cruz, Santa Cruz, CA 95064, USA. booch@cse.usc.edu|Department of Computer Science, University of California, Santa Cruz, Santa Cruz, CA 95064, USA. booch@cse.usc.edu|Department of Computer Science, University of California, Santa Cruz, Santa Cruz, CA 95064, USA. booch@cse.usc.edu