Implementation Advantages

Using a hierarchy to implement behavior arbitration offers certain advantages:

Handling Complexity and Conflict:

Hierarchical structures are highly intuitive and hence easier to design and to diagnose. Very complex systems can be put together in a modular fashion. Additionally, in a hierarchy of behaviors, conflicts between them are greatly reduced by the more or less fixed priority preferences inherited in the structure.

Increasing Efficiency:

Efficiency is obtained by information sharing. Knowledge obtained or processed by behaviors higher in the hierarchy can be used by behaviors lower in the hierarchy. For example, in the intention generator, when control flows down to the behavior `eating', previously processed sensory information about surrounding obstacles (by the `avoiding obstacle' behavior) can be used when the focusser is activated to compute the motor preferences (see the next section or Section ) for performing the eating behavior.

Compared with distributed control structures, hierarchical control structures offer lower flexibility but higher controllability. In particular, hierarchical control involves a much smaller number of control parameters and hence makes it easy to converge to a desirable choice, while this is not necessarily true for distributed control.

Xiaoyuan Tu

January 1996