The ECO Model: Events + Constraints + Objects.

This document describes the rationale and design of a programming model based on events, constraints, and objects and the use of this model in the Moonlight project. It describes the inter-object communication or invocation mechanism, and the way in which concurrency, synchronisation, and timing properties are expressed and controlled. The invocation mechanism is unusual in that it is event-based. It encourages loose coupling among the objects and this supports a high degree of encapsulation for each object. Concurrency, synchronisation, and timing properties are expressed in a uniform way using constraints which may be associated with objects and events. We describe the way in which the abstractions of the ECO model are expressed at the language level, and the support for them which is required from the runtime code and the underlying system.