WSOL – A Language for the Formal Specification of Various Constraints and Classes of Service for Web Services

We are developing a language, Web Service Offerings Language (WSOL), for the formal specification of various constraints, management statements, and classes of service for Web Services. WSOL is an XML (Extensible Markup Language) notation compatible with WSDL (Web Services Description Language). A service offering in WSOL is a formal description of one class of service of a Web Service. It contains formal representation of various constraints: functional (pre-, post-, and futureconditions), Quality of Service (QoS, a.k.a. non-functional, extrafunctional), and access rights. It also contains management statements, such as statements about prices, monetary penalties, and management responsibilities. One Web Service can be associated with multiple service offerings. For easier specification of similar service offerings, WSOL enables specification of constraint groups (CGs) and constraint group templates (CGTs). We have also developed a format for representation of dynamic relationships between service offerings. WSOL service offerings are simple contracts and SLAs (Service Level Agreements) between Web Services. Describing a Web Service in WSOL, in addition to WSDL, enables monitoring, metering, and management of Web Services. The Web Service, its consumer, or one or more designated third parties (usually SOAP message intermediaries) can meter QoS metrics and evaluate constraints in WSOL service offerings. Further, manipulation of service offerings can be used for dynamic adaptation and management of Web Service compositions. In addition, WSOL supports selection of a more appropriate Web Service and service offering for particular circumstances. The main distinctive characteristics of WSOL, compared to recent related works, are its expressive power, features that reduce run-time overhead, and orientation towards management applications.