QoS aggregation in Web service compositions

For the composition of Web services non-functional characteristics are commonly considered criteria for finding and selecting available services. Our work focuses on a mechanism that determines the overall Quality-of-Service (QoS) of a composition by aggregating the QoS of the individual services. With aggregated QoS it can be verified whether a set of services satisfies the QoS requirements for the whole composition or not. The aggregation performed builds upon abstract composition patterns, which model basic structural elements of a composition like parallel paths, a sequence, or a looped execution. In this work we extend existing composition patterns with the abilities to consider dependencies between services. Furthermore we introduce, how to use the pattern-based aggregation in the monitoring process during run-time. We will explain how the data derived from the monitoring process can be used to calculate a more accurate aggregation of QoS for the composition.