Presentation-abstraction-control (PAC)
Presentation-abstraction-control (PAC) is an architectural pattern for structuring interactive software systems as a hierarchy of cooperating agents. Each agent is itself divided into three parts: a presentation component, which is the agent’s user interface; an abstraction component, which handles the agent’s domain logic and data; and a control component, which mediates between the two and coordinates the agent with its parent and child agents in the hierarchy.
PAC is often compared to model-view-controller (MVC), the more widely known pattern it resembles at the level of a single agent. The key difference is PAC’s hierarchical structure. Rather than one presentation-abstraction-control triad covering a whole application, a PAC system is composed of many such triads arranged as a tree, each agent responsible for one part of the interface and free to coordinate with its neighbors only through its own control component. This makes PAC better suited than MVC to systems built from several semi-independent, composable interactive parts.