Andreas Heil describes the holistic approach to application development for complex software systems in web engineering. Based on the WebComposition methodology, the author examines an iterative development process, particularly for intelligent environments and distributed systems. The focus is on the efficient and cost-effective integration of hardware and software components using web technologies and the Semantic Web. The formal description method WebComposition-Concurrency-System enables efficient planning and monitoring of both the development and the operational operation of the system.