Top-down development of layered fault tolerant systems and its problems — a deontic perspective

Abstract

Although the top-down development paradigm has successfully been applied to master the complexity of large systems, it has not yet been accepted as a useful paradigm for fault tolerant system design. This is mainly due to a problem that is sometimes referred to as the “lazy programmers” paradox. The “lazy programmer” paradox was already present and solved in top-down development methods for non-critical systems. However, the problem has re-appeared in an even more serious variant for critical systems. A few “toy” examples concerning exception handling in an Ada-like language are used to explain and illustrate the paradox. One possible solution to the problem is to use a specification language in which one can express that certain behaviours of a system are preferred over others. This paper proposes deontic logic as such a specification language. Therefore, a short and rather informal introduction to deontic logic is included. A non-trivial example is included to illustrate how deontic logic can be used to solve the “lazy programmer” paradox.