1. Professor, Dept. of Architecture + Design, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061 (corresponding author).
2. Associate Professor, Dept. of Computer Science, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061.
3. Software Design Engineer, Microsoft Corporation; formerly Graduate Student, Dept. of Computer Science, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061.