Architectural Aspects

Architectural Aspects

The differences between various Hybrid Deliberative/Reactive architectures
fall into three areas based on how they answer the following questions: How
does the architecture distinguish between reaction and deliberation? How does it
organize responsibilities in the deliberative portion? How does the overall behavior
emerge? The difference between reaction and deliberation is a critical issue in
building a successful, reusable object-oriented implementation. This deter-

mines what functionality goes in what modules, what modules have access
to global knowledge (which leads to specifying public and friend classes
in C++), and what that global knowledge (shared data structures) should
be. Likewise, it is important to subdivide the deliberative portion into modules
or objects. A good decomposition will ensure portability and reusability.
While Hybrid architectures are most noteworthy for how they incorporate
deliberation into mobile robotics, they also introduce some changes in
the way reaction is organized. Many researchers found the two primary
means of combining reactive behaviors—subsumption and potential field
summation—to be limited. Since then at least three other mechanisms have
been introduced: voting (in theDAMNarchitecture), 121 fuzzy logic (Saphira), 77
and filtering (SFX).107
The number of Hybrid architectures is rapidly increasing. This section
attempts to introduce some conceptual organization on Hybrids in twoways.
First, it offers a set of common components—essentially, things to look for in
a Hybrid architecture. Second, it divides Hybrid into three broad categories:
managerial, state hierarchies, and model-oriented.