Coordination of Active Objects by Means of Explicit Connectors

Although coordination of multiple activities is a fundamental goal of object-oriented concurrent programming languages, there is only limited support for its specification and abstraction at the language level. This leads to a mismatch between conceptional designs, using high-level abstractions, and the implementation, using the low-level coordination constructs. Often coordination is hard-wired into the components they coordinate, which leads to evolution, maintenance and composibility problems. We propose a model called FLO/C that relies on the notion of connectors. A connector is an entity that enforces the coordination of the entities it coordinates. This model supports a clear separation between the coordinated active objects and their coordination. An active object only defines specific domain information and a connector only defines coordination between a group of active objects (its participants). The coordination is abstractly defined refering to components in terms of the object interface. Coordination and coordinated entities are independant and can evolve separately. Coordination can be composed and replaced easily.