The Role of Data in Safety-Related Systems

When considering the production of a computer-based system, it is common to partition the arrangement into hardware and software elements. The software part of such an arrangement is taken to include both the instructions that are executed by the processor, and the data that is used and produced by these instructions. In some cases, a large amount of data forms an essential element within the system and plays a vital role in ensuring its correct operation. In such situations it is perhaps more appropriate to partition a system into hardware, software and data, to allow appropriate importance to be given to each element. This is particularly appropriate in safety-related applications where the safe operation of the system is dependent upon the correctness of the data. Unfortunately, the various standards and guidelines that relate to the production of critical systems are concerned almost exclusively with methods of ensuring the ‘safety ’ of the hardware and the executable portions of the software of a system, and say almost nothing about the nature, production or testing of the data. This paper looks at the nature of data in a range of safety-critical applications. It then considers the characteristics of data faults and proposes a systematic approach to tackling them