On the Dynamic Manipulation of Classes of Service for XML Web Services

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. For their formal representation for XML (Extensible Markup Language) Web Services, we have developed the Web Service Offerings Language (WSOL). A service offering in WSOL is a formal description of one class of service of a Web Service. It contains various constraints (functional, QoS, access rights), management statements (e.g., prices, monetary penalties, and management responsibilities), and reusability constructs (determining static relationships between service offerings). One Web Service can be associated with multiple service offerings. Dynamic (i.e., run-time) relationships between service offerings are specified outside WSOL service offerings, in a special format. In addition to the WSOL language, we are developing the Web Service Offerings Infrastructure (WSOI) that addresses monitoring and accounting of WSOL service offerings and dynamic adaptation of Web Service compositions using manipulation of service offerings. Five mechanisms for the dynamic manipulation of service offerings are explored: switching (initiated by the consumer or the provider Web Service), deactivation, reactivation, deletion, and creation of service offerings. WSOL relationships between service offerings are particularly useful for these mechanisms. From analytical studies and practical experiments with dynamic adaptation scenarios involving WSOL and alternative approaches, we conclude that manipulation of classes of service is simpler and faster than recomposition of Web Services and re-negotiation of SLAs. While it has limitations, it can be a useful additional lightweight dynamic adaptation approach.