Specifying a real-time kernel

The application of formal methods to a safety-critical system is illustrated. The objective of the study was to improve the existing documentation of a diagnostic X-ray machine to serve later reimplementations. The separation of the kernel from applications helped identify a design flaw in the kernel that could have caused damage by the X-ray application. The case study which shows that mathematical techniques have an important role to play in documenting systems and avoiding design flaws, is a good example of the use of the Z (pronounced ´Zed´) notation and its methods for modeling systems. The limitations of this specification are delineated, showing that there is a need for other specification techniques to tackle the remaining properties, like real-time performance, for completeness and comparison.<>