Class declarations define new reference types and describe how they implement agents and components. Every class must implement either an Agent or Component or extend a class that implements an Agent or Component. A class that implements an agent is different from a class that implements a component. A class that implements a component describes its behavior, either by composing member components using connectors or by logic implemented in its methods, whereas a class that implements an agent makes use of connectors and channels to describe the behavior of a composite system where the agent composes components using connectors and communicates with other agents using channels.