To tackle the growing complexity of engineered systems, Model-Driven Engineering (MDE) proposes to promote models to first-class citizens in the development process. Within MDE, Multi-Paradigm Modelling (MPM) advocates modelling every relevant aspect of a system explicitly, using the most appropriate formalism (s), at the most appropriate level(s) of abstraction, while explicitly modelling the underlying process. Often, activities of the process require interaction with (domain-specific) engineering and modelling tools. These interactions are, however, typically captured in scripts and program code, which is ill-suited for describing the timed, reactive, and concurrent behaviour of these protocols. Additionally, formal analysis of the overall process is limited due to the incorporation of black-box activities. In this paper, we propose an approach for the explicit modelling of service interaction protocols in the activities of MDE processes. We also explicitly model the execution semantics of our process model, to promote reuse and allow for future analysability. For both purposes, we propose to use SCCD, a Statecharts variant, resulting in a unified and concise formalism.