Monitoring Interfaces for Faults

We consider the problem of a module interacting with an external interface (environment) where the interaction is expected to satisfy some system specification Φ. While we have the full implementation details of the module, we are only given a partial external specification for the interface. The interface specification being partial (incomplete) means that the interface displays only a strict subset of the behaviors allowed by the interface specification. Based on the assumption that interface specifications are typically incomplete, we address the question of whether we can tighten the interface specification into a strategy, consistent with the given partial specification, that will guarantee that all possible interactions resulting from possible behaviors of the module will satisfy the system specification Φ. We refer to such a tighter specification as Φ-guaranteeing specification. Rather than verifying whether the interface, which is often an off-theshelf component, satisfies the tighter specification, the paper proposes a construction of a run-time monitor which continuously checks the existence of a Φ-guaranteeing interface. We view the module and the external interface as players in a 2-player game. The interface has a winning strategy if it can guarantee that no matter what the module does, the overall specification Φ is met. The problem of incomplete specifications is resolved by allowing the interface to follow any strategy consistent with the interface specification. Our approach essentially combines traditional run-time monitoring and static analysis. This allows going beyond the focus of traditional run-time monitoring tools – error detection in the execution trace, towards the focus of the static analysis – bug detection in the programs. 1 This research was supported in part by NSF grant CCR-0205571 and ONR grant N0001499-1-0131. 2 Email: {amir,zaks}@cs.nyu.edu 3 Email: {[email protected] This is a preliminary version. The final version will be published in Electronic Notes in Theoretical Computer Science URL: www.elsevier.nl/locate/entcs