1. PhD Candidate, School of Computer Science, Carnegie Mellon Univ., Pittsburgh, PA 15213.
2. Post Doctoral Fellow, Civil Engineering, Dept. Carnegie Mellon Univ., Pittsburgh, PA 15213.
3. Alan J. Perlis Professor of Computer Science, School of Computer Science, Carnegie Mellon Univ., Pittsburgh, PA 15213.
4. Associate Professor, Electric Engineering, Dept., Carnegie Mellon Univ., Pittsburgh PA 15213.
5. Professor, School of Computer Science, Carnegie Mellon Univ., Pittsburgh PA 15213.