Abstract
We investigate the problem of locally monitoring contract regulated behaviours in agent-based web services. We encode contract clauses in service specifications by using extended timed automata. We propose a non intrusive local monitoring framework along with an API to monitor the fulfillment (or violation) of contractual obligations. A key feature of the framework is that it is fully symbolic thereby providing a scalable solution to monitoring. At runtime execution steps generated by the service are passed as input to the runtime monitor. Conformance of the execution against the service specification is checked using a symbolically represented extended timed automaton. This allows us to monitor service behaviours over large state spaces generated by multiple, long running contracts. We illustrate our methodology by monitoring a service composition scenario from the vehicle repair domain, and report on the experimental results.