Monitoring flow of web services in dynamic composition using event calculus rules

Monitoring composition of web services is important to ensure provisioning of a valid business process. Most of the existing works on service monitoring focused either on QoS violations or service interactions during execution of services that are statically composed. However, dynamic composition of services wherein the services are discovered and composed at runtime based on user requirements and outcome of previously composed services is significant for business applications with frequently changing user requirements and business policies. In such scenarios, the order in which the services are composed must be monitored to comply with business polices. Otherwise, the composition leads to incorrect and inconsistent results. To address this issue, a runtime monitoring framework is proposed in this paper that monitors composition order of services that are dynamically composed, validates it using predefined rules and initiates corrective actions in case of violations from rules. The web services and the rules for composition flow have been expressed as event calculus axioms that are useful in validating the composition order. The performance of the proposed framework has been assessed and it is found out that it introduces only a marginal overhead on turnaround time of the user request as compared to absence of monitoring.