A methodology for co-design based on a healthcare case study

Systems upon which a high degree of reliance can be asserted form the class of dependable systems. We present here a development method for a subclass of dependable systems, safety-critical control systems. This method supports simultaneous design of both hardware and software in a system where failures would cause significant losses. The method is based on using mathematically solid techniques that allow us to address safety and reliability issues early in the development cycle. We start with an abstract specification of the system and subsequently add details concerning functionality, safety and reliability in a stepwise manner. From the obtained specification we can deduce which parts of the system are implemented using software and which using hardware. We then decompose the specification into controller, sensors, actuators and plant. We use the formal development method B-action systems for our development process. The method has a good mechanised support via the tools associated with the B Method. We illustrate the development process on a medical laboratory device, i.e. a control oriented case study that is part of a healthcare system.