larity abstractions attached to the architectural aspects. A crosscutting interface is different from a module interface in the sense that the latter essentially provides services to other components. Crosscutting interfaces provide services to the system, but also specify when and how an aspect affects other architectural components. Contrary to interfaces in traditional architecture styles, they flexibly determine which external components and interfaces the architectural aspect of a software agent will be connected. With this dependency inversion, crosscutting interfaces overcome the problems associated with the rigidness implicit in traditional architectural styles (see Figure 1). Each agent’s architectural aspect can be more flexibly composed with the agent kernel and with any agent aspects depending on the requirements of a specific agent architecture.

(b) Tangling in a class representing an agent.

modularize with existing architectural abstractions. An aspect-oriented architectural style brings to the software architects a new abstraction, the notion of architectural aspects, and new composition means for handling each crosscutting agent concern as an individual component at an early stage of design, as illustrated in Figure 3a. Each architectural aspect modularizes a typical crosscutting agent property and separates it from the agent kernel. The “aspectization” of agent architectures allows the association of agenthood properties with the basic functionality in a way that is transparent to the agent kernel.

The key idea to enable adjustable compositions is the notion of crosscutting interfaces, which are modu-

Each of the architectural aspects is related to more than one component, representing the crosscutting nature of agent properties in complex architectures. An agent’s architectural aspect can realize more than one crosscutting interface since it can crosscut multiple agent components in different ways. The interface of an architectural aspect can crosscut the Kernel component and other architectural aspects. An aspect interface crosscuts either the internals of an agent component or elements of other interfaces. The first case means the architectural aspect affects the internal structure or dynamic behavior of an agent component. The second case means the aspect affects elements of an interface.

Instances of aspect-oriented agent architectures are illustrated for a user agent (see Figure 3a) and an information agent (see Figure 3b). Extensions of UML are used to represent the architectural aspects (compo-

Figure 2. Heterogeneous agent architectures: Crosscutting the life-cycle artifacts.