We present a component-based description language for heterogeneous systems composed of several data flow processing components and a unique event-based controller. Descriptions are used both for generating and deploying implementation code and for checking safety properties on the system. The only constraint is to specify the controller in a synchrounous reactive language. We propose an analysis tool which transforms temporal logic properties of the system as a whole into properties on the events of the controller, and hence into synchronous reactive observers. If checks succeed, the final system is therefore correct by construction. When it is not possible to generate observers that correspond exactly to the specified properties, our tool is capable of generating approximate observers. Alghough the results given by these are subject to interpretation, they can nevertheless prove useful and help detect defects or even guarantee the correctness of a system.