Separation of Concerns through Unif ication of Concepts1

Separation of concerns is a principle we apply to reduce complexity. This principle is especially important when it is used to separate stable from flexible parts of software systems to reduce the complexity of software evolution. We encapsulate the stable parts as components and the flexible parts as scripts. But there is a large range of requirements and consequent techniques available to achieve this separation. We propose a simple, unifying framework of forms, agents, and channels for modelling components and scripts. We have also developed an experimental composition language, called Piccola, based on this framework, that supports the specification of applications as flexible compositions of stable components.