Pattern-Oriented Software Architecture For Dummies

Chapter 14

Layering Interactive Agents with Presentation-Abstraction-Control

In This Chapter

• Building a system of agents for an interactive application
• Assembling legacy display components
• Implementing the Presentation-Abstraction-Control architecture

In this chapter, I tell you about Presentation-Abstraction-Control (PAC), a pattern for structuring your interactive application when the parts are autonomous components with their own independent capabilities.

I refer to these autonomous components as agents, and I define an agent as a component that has these capabilities:

• It can receive events and forward them to other agents.
• It contains data structures that store the agent's information as well as the agent's state.
• It can perform at least the following computations:
  • Processing incoming events
  • Updating its own state
  • Generating new events that are sent to other agents

Agents may range in size from a single object to something as complex as a complete software system.

Note: This definition of agent is specific to this chapter. If you've read about agents elsewhere, you'll see that the definitions are related, but in this chapter, I don't talk about anything more advanced than what I outline above.