Models are central to building confidence in cyber-physical systems. Simulation models, abstractions, and formal models all augment classical software engineering techniques such as object-oriented design to catch errors and to make software more modular and composable. Every formal model lives within a modeling framework that gives semantics to the model, and many modeling frameworks have been developed that enable rigorous analysis and proof of properties. But every such modeling framework is an imperfect mirror of reality. A computer system and a physical plant operating in the physical world may or may not accurately reflect behaviors predicted by a model, and the model may not reflect behaviors that are critical to correct operation of the system. Software in a cyber-physical system, for example, has timing properties that are rarely represented in formal models. In this talk, I will examine the limitations in the use of models. I will show that two very different classes of models are used in practice, classes that I call "scientific models" and "engineering models." These two classes have complementary properties, and many misuses of models stem from confusion about which class is being used.

Edward A. Lee is Professor of the Graduate School and Robert S. Pepper Distinguished Professor Emeritus in EECS at UC Berkeley. He is the author of several books and more than 300 papers and has delivered more than 170 keynote and other invited talks at venues worldwide. Lee's research focuses on cyber-physical systems, which integrate physical dynamics with software and networks.

His focus is on the use of deterministic models as a central part of the engineering toolkit for such systems. He is the director of iCyPhy, the Berkeley Industrial Cyber-Physical Systems Research Center, and the director of the Berkeley Ptolemy project. From 2005-2008, he served as chair of the EE Division and then chair of the EECS Department at UC Berkeley. He led the development of several influential open-source software packages, notably Ptolemy and its spinoffs. From 1979 to 1982 he was a member of technical staff at Bell Labs in Holmdel, New Jersey. He is a co-founder of BDTI, Inc. and has consulted for a number of other companies. He is a Fellow of the IEEE, was an NSF Presidential Young Investigator, won the 1997 Frederick Emmons Terman Award for Engineering Education, received the 2016 Outstanding Technical Achievement and Leadership Award from the IEEE Technical Committee on Real-Time Systems (TCRTS) and The Berkeley Citation in 2018.