He previously was a principal scientist at AT&T Bell Laboratories. He holds a Ph.D. and M.Sc. in computer science from the University of Toronto, and a M.Sc. in physics from Delft University of Technology. His research has covered many areas in artificial intelligence and computer science, including tractable inference, knowledge representation, natural language understanding, stochastic search methods, theory approximation, knowledge compilation, planning, default reasoning, and the connections between computer science and physics (phase transition phenomena). He has received four best paper awards at the American and Canadian national artificial intelligence conferences, and at the International Conference on Knowledge Representation. He holds an NSF CAREER Award and is an Alfred P. Sloan Research Fellow.