I. Introduction
Service-oriented architectures (SOA) deal with the growing need for distributed applications, not only support the integration and collaboration among departments of the same organization but also enable industrial partnerships across distinct organizations. Nowadays numerous Web services are put on the internet, of which some may have the same functionalities, but with different non-functional properties. Moreover, due to the limitation of a single Web service, Web services usually need to be composed as workflows (i.e., service processes) to satisfy customer's complex requirements or to mash up data from different data resources by using business process description languages, such as BPEL [1] and ORC [2]. So, there are a number of ongoing research works concerning quality-aware services composition [3], [4]. Particularly Automatic Service Composition (ASC) has been well addressed [5], [6], which can alleviate the workload of system exploitation by deeper level of service reuse.