The Previous State of the Art

The last decade of research has shown impressive convergence on the gross characteristics of software architectures for CCA. The field is now dominated by `hybrid', three-layer architectures (22,19). These hybrids combine the following:

1. behavior-based AI (BBAI), the decomposition of intelligence into simple, robust, reliable modules,
2. reactive planning, the ordering of expressed actions via carefully specified program structures, and
3. (optionally) deliberative planning, which may inform or create new reactive plans, or, in principle, even learn new behaviors.

In this section I will discuss these systems and their history in more detail. The remainder of this chapter presents an improvement to three-layer architectures, called Behavior-Oriented Design.