Service offerings for xml web services and their management applications

• Authors: Bernard Pagurek;Vladimir Tosic
• Venue: Service offerings for xml web services and their management applications
• Year: 2004

I show why the specification, monitoring, and dynamic (run-time) manipulation of classes of service are useful for XML (Extensible Markup Language) Web Services and how to achieve them. Classes of service are a mechanism for differentiation of service and quality of service (QoS) that incurs less overhead than custom-made Service Level Agreements (SLAs), user profiles, and other alternatives. A service offering is a formal description of one class of service of a Web Service. One Web Service can provide multiple service offerings. For formal specification of service offerings, I developed the Web Service Offerings Language (WSOL), compatible with the standard Web Services Description Language (WSDL). A WSOL service offering can contain descriptions of various categories of constraints, management statements, and reusability constructs. Dynamic relationships between service offerings are specified outside WSOL service offerings, in a special format. Describing a Web Service in WSOL enables monitoring, metering, and management of Web Services and their compositions. The main distinctive characteristics of WSOL, compared to related works, are its expressive capabilities, features with relatively low run-time overhead, and support for management applications. To achieve dynamic adaptation of a Web Service composition without breaking it, I developed algorithms and protocols for switching (consumer- and provider-initiated), deactivation, reactivation, deletion, and creation of service offerings. I analytically and experimentally compared these manipulation mechanisms with re-composition of Web Services and re-negotiation of SLAs and concluded that the proposed mechanisms are, in principle, simpler, faster, and with lower run-time overhead.The Web Service Offerings Infrastructure (WSOI) measures and calculates used QoS metrics, evaluates WSOL constraints, and performs accounting of executed operations and evaluated constraints. These monitoring activities can be performed by providers, consumers, or management third parties (SOAP intermediaries or probes). One of the main differences between WSOI and the other Web Service management, infrastructures are the modules, data structures, and specialized management operations implementing the mechanisms for manipulation of service offerings. The WSOI prototype extends the open-source Apache Axis SOAP engine. Its additional overhead is relatively low. The results of this research can be used in future Web Service standards and products.