SOFTWARE DIVERSITY - PRACTICAL STATISTICS FOR ITS MEASUREMENT AND EXPLOITATION

The topic of this paper is the exploitation of diversity to enhance co mputer system reliability. It is well established that a diverse syste m composed of multiple alternative versions is more reliable than any single version alone, and this knowledge has occasionally been exploit ed in safety-critical applications. However, it is not clear what this property is, nor how the available diversity in a collection of versi ons is best exploited. We develop, define, illustrate and assess diver sity measures, voting strategies for diversity exploitation, and inter actions between the two. We take the view that a proper understanding of such issues is required if multiversion software engineering is to be elevated from the current ''try it and see'' procedure to a systema tic technology. In addition, we introduce inductive programming techni ques, particularly neural computing, as a cost-effective route to the practical use of multiversion systems outside the demanding requiremen ts of safety-critical systems, i.e. in general software engineering. ( C) 1997 Elsevier Science B.V.