Using Four-Valued Signal Temporal Logic for Incremental Verification of Hybrid Systems

Hybrid systems are often safety-critical and at the same time difficult to formally verify due to their mixed discrete and continuous behavior. To address this issue, we propose a novel incremental verification algorithm for hybrid systems based on online monitoring techniques and reachability analysis. To this end, we develop a four-valued semantics for signal temporal logic that allows us to distinguish two types of uncertainty: one arising from set-based evaluation and another one from the incremental nature of our algorithm. Using these semantics to continuously update the verification verdict, our verification algorithm is the first to run alongside the reachability analysis of the system to be verified. This makes it possible to stop the reachability analysis as soon as we obtain a conclusive verdict. We demonstrate the usefulness of our novel approach by several experiments.