Self-expression and Dynamic Attribute-Based Ensembles in SCEL

In the field of distributed autonomous computing the current trend is to develop cooperating computational entities enabled with enhanced self-* properties. The expression self-* indicates the possibility of a component inside an ensemble, i.e. a set of collaborative autonomic components, to self organize, heal repair, optimize and configure with little or no human interaction. We focus on a self-* property called self-expression, defined as the ability to deploy run-time changes of the coordination pattern of the observed ensemble; the goal of the ensemble is to achieve adaptivity by meeting functional and non-functional requirements when specific tasks have to be completed. The purpose of this paper is to rigorously present the mechanisms involved whenever a change in the coordination pattern is needed, and the interactions that take place. To this aim, we use SCEL Software Component Ensemble Language, a formal language for describing autonomic components and their interactions, featuring a highly dynamic and flexible way to form ensembles based on components' attributes.