A role-based coordination model and its realization

This paper presents a framework to support Open Distributed and Embedded (ODE) application development based on the Actor-Role-Coordinator (ARC) model. The ARC model is a role-based coordination model developed to address three main concerns inherent in an ODE system: dynamicity, scalability, and stringent QoS requirements. It treats an ODE system as a composition of concurrent computation and coerced coordination. In particular, the ARC model uses concurrent objects that communicate with each other through asynchronous messages, i.e., actors, to model the concurrent computation of an ODE system, while the system's QoS requirements are mapped to coordination constraints. Coordination entities, i.e., roles and coordinators, impose coordination constraints on concurrent actors transparently through message interceptions and manipulations. In the ARC model, roles provide actor behavior abstractions for coordinators and coordinators are responsible for coordinating roles. In addition, a role also has local coordination responsibilities among actors belonging to that role. This coordination is called intra-role coordination which complements the inter-role coordination performed by the coordinators. In other words, under the ARC model, an ODE application is modeled by three orthogonal layers: computation, intrarole coordination and inter-role coordination. This separation not only improves software modularity and reusability, but also allows different levels of compositions. Our experiments show that the model scales well as the number of entities involved in the system increases, and that the performance overhead introduced by the external coordination layers is limited.