The Indispensable Role of Rationale in Safety Standards

Abstract

In this paper, we argue that standards, especially those intended to support critical applications, should define explicitly both the properties expected to accrue from use of the standard and an explicit rationale that justifies the contents of the standard. Current standards do not include an explicit, comprehensive rationale. Without a rationale, the use, maintenance, and revision of standards is unnecessarily difficult. We introduce a new concept for standards, the rationalized standard. A rationalized standard combines: (a) an explicit goal defining a property desired for conformant systems, (b) guidance that, if followed correctly, should yield an entity with the property stated in the goal, and (c) the rationale showing the reasoning why there is assurance with reasonable confidence that a conformant entity will have the property defined by the goal. We illustrate the utility of an explicit rationale using an existing safety standard, ISO 26262.