A Cyber-physical System (CPS) can be described as a network of interlinked, concurrent computational components that interact with the physical world. Such a system is usually of reactive nature and must satisfy strict timing requirements to guarantee a correct behaviour. The components can be of mixed-criticality which implies different progress models and communication models, depending whether the focus of a component lies on predictability or resource efficiency. In this dissertation I present a novel approach that bridges the gap between stream processing models and Labelled Transition Systems (LTSs). The former offer powerful tools to describe concurrent systems of, usually simple, components while the latter allow to describe complex, reactive, components and their mutual interaction. In order to achieve the bridge between the two domains I introduce the novel LTS Synchronous Interface Automaton (SIA) that allows to model the interaction protocol of a process via its interface and to incrementally compose simple processes into more complex ones while preserving the system properties. Exploiting these properties I introduce an analysis to identify permanent blocking situations in a network of composed processes. SIAs are wrapped by the novel component-based coordination model Process Network with Synchronous Communication (PNSC) that allows to describe a network of concurrent processes where multiple communication models and the co-existence and interaction of heterogeneous processes is supported due to well defined interfaces. The work presented in this dissertation follows a holistic approach which spans from the theory of the underlying model to an instantiation of the model as a novel coordination language, called Streamix. The language uses network operators to compose networks of concurrent processes in a structured and hierarchical way. The work is validated by a prototype implementation of a compiler and a Run-time System (RTS) that allows to compile a Streamix program and execute it on a platform with support for ISO C, POSIX threads, and a Linux operating system.