Abstract

The notion of real-time reactive behavior encompasses concurrency, communication through sensors and actuators, and relations between input and output over time. Real-time reactive systems are inherently complex, and often used in safety-critical contexts. Application domains include control systems for nuclear reactors, air traffic, railroad crossing, telecommunications, and medical devices. Applying formal methods in the development process is seen as a means for dealing with the complexity, and for quality assurance. One of the goals is to formally verify time-dependent safety properties in the design. The scope of this thesis encompasses three major components. We develop a visual technique for object-oriented modeling of real-time reactive systems, based on a minimal set of extensions to UML, along with a set of well-formedness rules for the real-time models. We then present a formalization of the Real-Time rules of UML metamodel, and provide formal denotational and operational semantics for RTUML. Finally, we introduce a methodology for mechanized verification of time-dependent properties in the RTUML design of real-time reactive systems, within the PVS verification environment. The formal semantics of RTUML provides a foundation for the verification methodology, and for rigorous analysis and validation techniques. The novelty of the development methodology for real-time systems lies in the mechanized verification approach superimposed on the object-oriented modeling technique.