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The method, called Model Checking, is the most widely used technique for detecting and diagnosing errors in complex hardware and software design. It has helped to improve the reliability of complex computer chips, systems and networks.

Clarke, a professor at Carnegie Mellon University, Emerson, of the University of Texas, Austin, and Joseph Sifakis of the University of Grenoble, will share $250,000. The Turing Award, presented annually by the Association for Computing Machinery, is considered to be the most prestigious award in computing. Often referred to as "the Nobel Prize of computing," it is named for British mathematician Alan M. Turing

Model Checking is a type of "formal verification" that analyzes the logic underlying a design, much as a mathematician uses a proof to determine that a theorem is correct. Far from hit or miss, Model Checking considers every possible state of a hardware or software design and determines if it is consistent with the designer's specifications. Clarke and Emerson originated the idea of Model Checking at Harvard in 1981. They developed a theoretical technique for determining whether an abstract model of a hardware or software design satisfies a formal specification, given as a formula in Temporal Logic, a notation for describing possible sequences of events. Moreover, when the system fails the specification, it could identify a counterexample to show the source of the problem. Numerous model checking systems have been implemented, such as Spin at Bell Labs.

Clarke implemented the first Model Checker in 1982. It could analyze all the possible states of a given circuit, but was limited to relatively small designs -- much smaller than the systems being built by computer manufacturers. In 1987, Clarke's graduate student, Kenneth McMillan, realized that he could implement Model Checking by a series of operations on binary decision diagrams (BDDs), a method of representing symbolic information that had recently been developed by another Carnegie Mellon computer science professor, Randal E. Bryant. This new system, called "Symbolic Model Checking," was able to analyze billions of billions of states, making it relevant to commercial computer design problems and leading to its widespread adoption by the industry. For this invention, Bryant, Clarke, Emerson and McMillan won the 1998 Paris Kanellakis Award for Theory and Practice from the ACM. In 1999, they also received the Allen Newell Award for Research Excellence from CMU.

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