Conclusions

Abstract

In this book, we have, for pedagogical reasons, introduced problems and solutions in a progressive way, providing separated viewpoints on the design of dependable computing systems. In this concluding chapter, with the same pedagogical objectives, we will first make a synthesis of the numerous aspects we have encountered. This synthetic view is now necessary to reorder the most important notions explained in the preceding chapters. Section 19.1 summarizes the needs and the impairments which are at the origin of studies on dependability. In section 19.2, we consider the three classes of protective means introduced to obtain dependable products: fault prevention, fault removal, and fault tolerance. For each of these classes, we have studied numerous techniques. The question of their respective efficiency is now addressed. These techniques aim at increasing the dependability, that is the reliance that can justifiably be placed on the service delivered. Hence, we must evaluate them using the dependability attributes and assessment techniques discussed in section 19.3. We analyze here only three attributes of the quantitative approaches: the redundancy which deals with the structure of the product and/or its intermediate models, the reliability and the safety. An overview of the qualitative approaches is then provided.