The description and calculation of quality of composite services 1

With the widespread of Web services (WS), more deployed services are being registered into a services registry, consequently giving rise to a series of problems. A conspicuous one is the large amount of functionally equivalent Web services returned by a service registry. A plausible solution is to involve QoS (quality of service) in the services discovery. However, some existing QoS-based discovery mechanisms still fail to consider two distinct points. Firstly, most solutions involve poor semantics so different parties may have different understandings of the same QoS metric. Secondly, existing QoS metrics of WS are so numerous, ambiguous and unpredictable that it limits the flexibility and expansibility. To address these two problems, this paper presents a novel and extensible ontology-based approach for description of the QoS constraints. Further, we propose a QoS calculation method for the composite service to judge whether the set of recommended services is qualified for the QoS constraints.