Structured methods for real-time systems [44,141] originated in systems analysis methods used in industry starting a decade ago. These methods provide a structured set of system (read: controller) requirements. The system requirements specify what problem the controller must solve, and how the controller must be structured.
The system requirements includes various views and layers of the controller such as (a) data flow diagrams to decompose the controller, its functions and its flow of data, (b) control flow diagrams (enhanced state transition diagrams) to represent the system dynamics, (c) a requirements dictionary which is an alphabetical listing of all inputs, outputs, data and control flows, and (d) a table of response times in which the incoming and outgoing events (from and to the plant) are listed with their respective repetition rates or response times. The timing requirements are not particularly well integrated with the rest of the requirements.
These methods have been used with some success in actual industrial applications. However, these methods have no formal semantics. The resulting controller design cannot be executed for simulated behaviour, nor can they be compiled into code (e.g. into Ada or C). There is no support for formal verification. Nondeterministic plant behaviour cannot be suitably modelled.