It is not uncommon, particularly in the early literature in computer science, to equate concurrency with nondeterminism and to treat the two together as a profound difficulty encountered when trying to understand programs. This makes the title of this talk an oxymoron. Nondeterminism is often defined for programs as exhibiting “observably different behavior given the same inputs.” But nearly all programs exhibit observably different behavior given the same inputs. For example, the time at which an output is produced is observably different for all but the most stringent real-time systems. In practice, unless you are designing such a real-time system, you are unlikely to consider the timing of the output part of the “behavior.” What about the timing of the inputs? In this talk, I argue for interpreting determinism as a property of models, not as a property of physical systems. I will then argue that, contrary to almost all current practice, determinism has immense value in concurrent and distributed software systems. Moreover, I will show that deterministic models do not intrinsically come with a performance penalty and that they make the design of fault-tolerant systems easier, not harder.

Edward A. Lee is Professor of the Graduate School and Distinguished Professor Emeritus in Electrical Engineering and Computer Sciences (EECS) at the University of California at Berkeley, where he has been on the faculty since 1986. He is co-founder of BDTI, Inc. and Xronos Inc. He is the author of seven books, some with several editions, including two for a general audience, and hundreds of papers and technical reports. Lee has delivered hundreds of keynote and other invited talks at venues worldwide and has graduated 40 PhD students. Professor Lee’s research group studies 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. From 2005-2008, he served as Chair of the EE Division and then Chair of the EECS Department at UC Berkeley. He has led the development of several influential open-source software packages, notably Ptolemy and Lingua Franca. He received his BS degree in 1979 from Yale University, with a double major in Computer Science and Engineering and Applied Science, an SM degree in EECS from MIT in 1981, and a Ph.D. in EECS from UC Berkeley in 1986. From 1979 to 1982 he was a member of technical staff at Bell Labs in Holmdel, New Jersey, in the Advanced Data Communications Laboratory. 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), the 2018 Berkeley Citation, the 2019 IEEE Technical Committee on Cyber-Physical Systems (TCCPS) Technical Achievement Award, the 2022 European Design and Automation Association (EDAA) Achievement Award, the 2022 ACM SIGBED Technical Achievement Award, an Honorary Doctorate in Computer Science from the Technical University of Vienna in 2022, the 2023 CASES Test of Time Award for a 2008 paper, the 2024 HiPEAC Technology Transfer Award, the HSCC 2026 Test of Time Award for a 2005 paper, and the ICCPS 2026 Test-of-Time Award for 2013 paper.