Scalable Service Selection for Web Service Composition Supporting Differentiated QoS Classes ∗

A composite Web service can be constructed and deployed by combining independently developed component services, each one may be offered by different providers with different non-functional Quality of Service (QoS) attributes. Therefore, a selection process is needed to identify which constituent services are to be used to construct a composite service that best meets the QoS requirements of its users. In this paper, we consider a service broker that offers a composite service characterized by differentiated QoS classes which imply diverse monetary prices. These QoS classes are settled on the basis of some Service Level Agreements (SLAs) that the broker negotiate with both the requestors and the service providers. Differently from most of the current approaches, which optimize independently the end-to-end QoS of single requests and often require the solution of an NP-hard problem for each request, we optimize the end-to-end aggregated QoS of all incoming flows of requests by means of a simple linear programming problem, which can be efficiently solved. As a result, the proposed approach is scalable and lends itself to an efficient implementation