Although web services are intended for short-term ad-hoc-collaborations, in practice, many Web service compositions are offered longterm to customers. While the Web services making up the composition may vary, the structure of the composition is rather fixed. For companies managing such Web service compositions, however, challenges arise which go far beyond simple bilateral contract monitoring. For example, it is not only important to determine whether or not a component (i.e., Web service) in a composition is performing properly, but also to understand what the impact of its performance is on the overall service composition.
In the MoDe4SLA project we have elaborated important requirements existing for the monitoring of service compositions. In particular, we provide a sophisticated approach for determining the impact each web service (of a composite service) has on the composition at runtime. More precisely, MoDe4SLA identifies complex dependencies between Service Level Agreements (SLAs) in a service composition. By explicating these dependencies, causes of SLA violations of a service might be explained by malfunctioning of the services it depends on. MoDe4SLA assists managers in identifying such causes.
We are also evaluating the MoDe4SLA approach concerning usefulness for the user as well as effectiveness for the business. Usefulness is evaluated by experts who are asked to manage simulated runs of service compositions using MoDe4SLA. Their opinion on the approach is an indicator for its usefulness. Effectiveness is evaluated by comparing runtime results of SLA management using MoDe4SLA with runtime results of unsupported management. Criteria for effectiveness are cost reduction and increase in customer satisfaction.