Ensuring Service Level Agreements for Service Workflows

Specifying and monitoring service level agreements (SLA) has been the subject of intensive research. However, methods of enforcing SLA have not addressed the specific issues of composite services (CS). Our work focuses on the problem of keeping prearranged SLAs for service workflows including workflows supporting long lived transactions (e.g. WS-BA). As a solution we offer scheduling of component service requests. The latter is based on regaining control over legacy services by means of transparent proxies and later scheduling of their invocations. Various heuristics based policies are evaluated under two different types of service level agreements. The policies vary from the simpler, operating only on the base of business value, to the more complex which also consider Quality of Service requirements, topologies of workflows, utilization of components services, etc. The experiments conducted over the model, which precisely captures the behavior of web services, reveal the benefits of providing schedulers with various types of context.