Principles of multi-level reflection for fault tolerant architectures

We present the principles of multi-level reflection as an enabling technology for the design and implementation of adaptive fault tolerant systems. By exhibiting the structural and behavioral aspects of a software component, the reflection paradigm enables the design and implementation of appropriate non-functional mechanisms at a meta-level. The separation of concerns provided by reflective architectures makes reflection a perfect match for fault tolerance mechanisms. However, in order to provide the necessary and sufficient information for error detection and recovery, reflection must be applied to all system layers in an orthogonal manner. This is the main motivation behind the notion of multi-level reflection that is introduced. We describe the basic concepts of this new architectural paradigm, and illustrate them with concrete examples. We also discuss some practical work that has recently been carried out to start implementing the proposed framework.