Service-oriented computing is an emerging paradigm where services are understood as autonomous, platform-independent computational entities that can be described, published, categorised, discovered, and dynamically assembled for developing massively distributed, interoperable, evolvable systems and applications. The IST-FET Integrated Project Sensoria aims at developing a novel comprehensive approach to the engineering of service-oriented software systems where foundational theories, techniques and methods are fully integrated in a pragmatic software engineering approach. In this paper we present first ideas for the Sensoria semantic-based development of service-oriented systems. This includes service-oriented extensions to the UML, a mathematical basis formed by a family of process calculi, a language for expressing context-dependent soft constraints and preferences, qualitative and quantitative analysis methods, and model transformations from UML to process calculi. The results are illustrated by a case study in the area of automotive systems.