Complex Web services are comparable to large software systems, thus their management and engineering process requires feasible and sophisticated methodologies and processes. Standard Web page editors and Web site management tools are not built for architecting complex services and cannot handle all tasks in the Web service engineering process. We introduced the JESSICA system to utilize object-oriented concepts for the Web service management. To support all stages of a service's life cycle, from the architectural design via the object-based JESSICA model definition to the implementation and maintenance of Web documents and dynamic server scripts, we propose an engineering environment for Web services. The approach consists of three components: the graphical editor JAZZ provides visual features to model the architecture with objects that abstractly describe the entire Web service in the Uniform Modeling Language UML. The object-oriented language JESSICA defines Web service components of any granularity and their internal and external relations based on the Extended Markup Language XML. A java-based compiler transfers the abstract service model into a consistent Web site. UML is used to support the decomposition of complex services into manageable units. The JESSICA system utilizes object-oriented concepts such as abstraction, encapsulation, inheritance, and reuse of commonalities. The strength of the engineering system lies in the combination of these three components in order to provide support for all stages in a Web service's life cycle. We demonstrate the feasibility of our process on the engineering of the Vienna International Festival Web site. Based on this reasonably sized case study we propose that the combination of UML and JESSICA improves Web service engineering and makes design, implementation and maintenance of complex services easier, faster, and less error-prone.