There are a number of methods available for describing processes, many of which are fairly informal, such as Block Diagrams or Flowcharts. These suffice in many circumstances but are inadequate in others, typically where the process is complex or a more rigorous approach is required. A problem which can arise when being more rigorous is that the overall understanding can be lost in the detail. The challenge is thus to find a method that is simultaneously precise and lucid at all levels.