Ten Years of Self-adaptive Systems: From Dynamic Ensembles to Collective Adaptive Systems

Self-adaptive systems have been introduced to manage situations where software systems operate under continuous perturbations due to the unpredicted behaviors of their clients and the occurrence of exogenous changes in the environment in which they operate. Adaptation is triggered by the run-time occurrence of an extraordinary circumstance, and it is handled by an adaptation process that involves components affected by the issue, and is able to handle the run-time modification of the structure and behavior of a running system. In this paper we report our experience gained in the last 10 years on models, techniques and applications in the field of self-adaptation. We present the various steps taken by means of a formal framework introduced to characterize the different aspects of an ensemble-based software engineering approach. We present (i) how to model dynamic ensembles using typed graph grammars, (ii) how to specialize and re-configure ensembles and, (ii) how to manage collective adaptations in an ensemble. All these aspects have been part of our research on self-adaptation and have been used to specify and deploy concrete solutions in different application domains.