The process notion is central in computing. Business processes and workflow processes are essential elements of software systems implementations. Processes are connected to notions of interaction and composition. The Web Services Framework as a development and deployment platform for services is based on the assembly of interacting processes as the compositional paradigm. Service-based software development on and for the Web platform embracing the philosophy of discovering and using third-party services makes a shared knowledge representation framework necessary. We develop a semantical and ontological framework for service process composition. We propose a framework for the compositional de�nition of Web services based on the �-calculus to de�ne protocol-like restrictions on service interactions and based on description logic and ontologies to guide the discovery and modelling of services and processes.