In the Service Oriented Architecture (SOA) complex applications can be described as business processes from independently developed services that can be selected at run time on the basis of the provided Quality of Service (QoS). However, QoS requirements are difficult to satisfy especially for the high variability of Internet application workloads. Autonomic grid architectures, which provide basic mechanisms to dynamically re-configure service center infrastructures, can be be exploited to fullfill varying QoS requirements. We tackle the problem of selection of Web services that assure the optimum mapping between each abstract Web service of a business process and a Web service which implements the abstract description, such that the overall quality of service perceived by the user is maximized. The proposed solution guarantees the fulfillment of global constraints, considers variable quality of service profile of component Web services and the long term process execution. The soundness of the proposed solution is shown trough the results obtained on an industrial application example. Furthermore, preliminary computational experiments show that the identified solution has a gap of few percentage units to the global optimum of the problem.