Improving the QoS of WS compositions based on redundant services

A composition arranges available services resulting in a defined flow of tasks. A discovery process identifies the suitable candidate services for a composition. A subsequent selection process chooses the optimal candidate for each task. The selection process can consider - if supported - different quality-of-service (QoS) categories of the individual services to optimize the quality of the whole composition. The result is a quality-optimized assignment of candidates to each task. This paper discusses how already identified candidates, which a selection process originally has separated out, can improve a composition w.r.t. particular QoS categories. To realize this improvement, redundant arrangements involve the alternative candidates in order to supplement the originally assigned service. We formed these redundant arrangements on the basis of our previously introduced compositions patterns. The contribution of this paper is a model which allows aggregating the resulting QoS of the composition when these arrangements are applied.