 He has taught at Yale University and the City University of New York.From 1977 to 2002 he was with the Artificial Intelligence Center at SRI International, Menlo Park, California, where he was a principal scientist and program director of the Natural Language Program.He has written numerous papers in the areas of parsing, syntax, semantic interpretation, information extraction, knowledge representation, encoding commonsense knowledge, discourse analysis, the structure of conversation, and the Semantic Web.