Filling In The Gaps : Efficient Techniques for Real Time Verification

Real time systems are a class of systems in whose evolution time plays an essential role. Examples of real time systems include controllers in various embedded systems, timed protocols. Standard timed model checking tools like UPPAAL and KRONOS are based either on the region graph construction or on the clock zone concept. Both these approaches treat clock variables differently from other state variables. An alternate approach is to discretize the continuous clock variables and thus treat them as any other state variable. We propose a new discretization method that provides a canonical representation for the discrete clock values. This results in significantly smaller state spaces compared to other discretization methods. Our discretization, which preserves continuous time semantics, also leads to a natural class of abstractions for real time systems. The abstract systems thus obtained simulate the discretized concrete systems and their state spaces are much smaller than the concrete systems. To mitigate the effect of large time constants, a known source of trouble for discretization based methods, we propose a technique called jumps that allows clock variables to advance in large increments. We include the results of our experiments on two previously studied real time examples to demonstrate the efficacy of our methods.

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