Third edition of Artificial Intelligence: foundations of computational agents, Cambridge University Press, 2023 is now available (including the full text).
2 Agent Architectures and Hierarchical Control
By a hierarchic system, or hierarchy, I mean a system that is
composed of interrelated subsystems, each of the latter being in
turn hierarchic in structure until we reach some lowest level of
elementary subsystem. In most systems of nature it is somewhat
arbitrary as to where we leave off the partitioning and what
subsystems we take as elementary. Physics makes much use of the
concept of "elementary particle," although the particles have a
disconcerting tendency not to remain elementary very long ...
Empirically a large proportion of the complex systems we observe in
nature exhibit hierarchic structure. On theoretical grounds we would
expect complex systems to be hierarchies in a world in which
complexity had to evolve from simplicity.
- Herbert A. Simon (1996)
This chapter discusses how an intelligent agent can perceive, reason, and act over time in an environment. In particular, it considers the internal structure of an agent. As Simon points out in the quote above, hierarchical decomposition is an important part of the design of complex systems such as intelligent agents. This chapter presents ways to design agents in terms of hierarchical decompositions and ways that agents can be built, taking into account the knowledge that an agent needs to act intelligently.
