For his 1992 Doctoral thesis, Ferguson developed the TOURINGMACHINES hybrid agent
architecture [Ferguson, 1992a][Ferguson, 1992b]
. The architecture
consists of perception and action subsystems, which
interface directly with the agent's environment, and three control layers, embedded in a control framework, which
mediates between the layers. Each layer is an independent,
activity-producing, concurrently executing process.
The reactive layer generates potential courses of action in response to events that happen too quickly for other layers to deal with. It is implemented as a set of situation-action rules, in the style of Brooks' subsumption architecture (see above).
The planning layer constructs plans and selects actions to execute in order to achieve the agent's goals. This layer consists of two components: a planner, and a focus of attention mechanism. The planner integrates plan generation and execution, and uses a library of partially elaborated plans, together with a topological world map, in order to construct plans that will accomplish the agent's main goal. The purpose of the focus of attention mechanism is to limit the amount of information that the planner must deal with, and so improve its efficiency. It does this by filtering out irrelevant information from the environment.
The modelling layer contains symbolic representations of the cognitive state of other entities in the agent's environment. These models are manipulated in order to identify and resolve goal conflicts - situations where an agent can no longer achieve its goals, as a result of unexpected interference.
The three layers are able to communicate with each other (via message passing), and are embedded in a control framework. The purpose of this framework is to mediate between the layers, and in particular, to deal with conflicting action proposals from the different layers. The control framework does this by using control rules.