Reflective fault-tolerant systems: from experience to challenges

This paper presents research work performed on the development and the verification of dependable reflective systems based on MetaObject Protocols (MOPS). We describe our experience, we draw the lessons learned from both a design and a validation viewpoint, and we discuss some possible future trends on this topic. The main originality of this work relies on the combination of both design and validation issues for the development of reflective systems, which has led to the definition of a reflective framework for the next generation of fault-tolerant systems. This framework includes: 1) the specification of a MetaObject Protocol suited to the implementation of fault-tolerant systems and 2) the definition of a general test strategy to guide its verification. The proposed approach is generic and solves many issues related to the use and evolution of system platforms with dependability requirements. Two different instances of the specified MOP have been implemented in order to study the impact of the MOP architecture in the development of a reflective fault-tolerant system. As far as the test strategy is concerned, a different testing level is associated with each reflective mechanism defined in the MOP. For each testing level, we characterize the test objectives and the required test environments. According to this experience, several new research challenges are finally identified.