PresentationAbstractionControl

Presentation-Abstraction-Control (PAC) is an architectural pattern used for designing interactive software with complex user interfaces. It emphasizes a clear separation of concerns by dividing the UI into three roles: presentation, abstraction, and control, and by organizing components into a hierarchical tree. This structure supports modular development, easier maintenance, and clearer boundaries between UI behavior and domain logic.

In a PAC component, the presentation is the visual and input layer and is responsible for rendering and user interaction. The abstraction represents the underlying data and domain objects relevant to that part of the UI. The control acts as the mediator and coordinator, handling user events, updating the abstraction, and instructing the presentation what to render. A UI can be composed of many PAC components in a tree, with each child PAC responsible for a subfunction.

Communication follows a defined sequence: the user interacts with the presentation, which sends events to the control; the control manipulates the abstraction and may request presentation updates; the abstraction notifies the control of state changes, prompting changes to the presentation. PAC supports nesting, so a parent PAC can control several child PACs and route events between them.

PAC is related to MVC and MVP patterns but provides a finer-grained separation and a centralized mediator role. It is particularly suitable for complex, distributed, or multi-window interfaces where modularity and independent development of UI regions are beneficial. Drawbacks include design complexity, potential performance overhead, and a steeper learning curve for teams unfamiliar with the pattern.