Towards partial monitoring: Never too early to give in

Runtime Verification is a lightweight formal verification technique used to verify whether a system behaves as expected at runtime. Expected behaviour is typically formally specified using properties, which are used to automatically synthesise monitors. Properties that can be verified at runtime by a monitor are called monitorable, while those that cannot are termed non-monitorable. In this paper, we revisit the notion of monitorability and demonstrate how non-monitorable properties can still be used to generate partial monitors. We tackle this from two different perspectives: (i) by recognising that a monitor can give up on monitoring the property under analysis if it recognises that the monitoring will never conclude the satisfaction or violation of the property; (ii) by recognising that a monitor can give up on events that are not necessary for successful monitoring of the property under analysis. By considering these two aspects, we present how to achieve partial monitoring of Linear Temporal Logic properties by building upon the standard monitor construction. Finally, we present a prototype implementation of our approach and its application to a remote inspection case study, as well as a set of evaluation experiments to stress test our approach using synthetic properties.