Conformal Quantitative Predictive Monitoring of STL Requirements for Stochastic Processes
This addresses runtime safety assurance for stochastic systems, offering a novel method for quantitative predictions with guarantees, though it is incremental in applying conformal inference to this domain.
The paper tackles the problem of predictive monitoring for runtime safety assurance by introducing quantitative predictive monitoring (QPM), which predicts quantitative Signal Temporal Logic satisfaction measures for stochastic processes with probabilistic guarantees, achieving efficient computation and scalability across benchmarks.
We consider the problem of predictive monitoring (PM), i.e., predicting at runtime the satisfaction of a desired property from the current system's state. Due to its relevance for runtime safety assurance and online control, PM methods need to be efficient to enable timely interventions against predicted violations, while providing correctness guarantees. We introduce \textit{quantitative predictive monitoring (QPM)}, the first PM method to support stochastic processes and rich specifications given in Signal Temporal Logic (STL). Unlike most of the existing PM techniques that predict whether or not some property $φ$ is satisfied, QPM provides a quantitative measure of satisfaction by predicting the quantitative (aka robust) STL semantics of $φ$. QPM derives prediction intervals that are highly efficient to compute and with probabilistic guarantees, in that the intervals cover with arbitrary probability the STL robustness values relative to the stochastic evolution of the system. To do so, we take a machine-learning approach and leverage recent advances in conformal inference for quantile regression, thereby avoiding expensive Monte-Carlo simulations at runtime to estimate the intervals. We also show how our monitors can be combined in a compositional manner to handle composite formulas, without retraining the predictors nor sacrificing the guarantees. We demonstrate the effectiveness and scalability of QPM over a benchmark of four discrete-time stochastic processes with varying degrees of complexity.