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5.5.4 Abstract behaviors 5 Designing a Reactive Implementation
Finite state automata are a useful tool for expressing the coordinated control
program of an abstract behavior. They fall short as a programming tool for
abstract behaviors in a number of ways. First, in many cases, the assemblage
of behaviors represents a prototypical sequence of events that should be
TEMPLATE slightly adapted to different situations, in essence, a template or abstract behav-
ABSTRACT BEHAVIOR ior. In the Pick Up the Trash event, recycling Coke cans was only part of the
task; the robots were also supposed to find white Styrofoam cups and deposit
them in yellow trash cans. The behaviors represented by the FSA could be
collected into an abstract behavior: pick-up-the-trash(trash-color,
trash can-color, size-trash can).
Second, templates need to handle different initialization conditions. Ini-
tialization wasn’t a big problem for the Pick Up the Trash task, but it could
be one for other applications. For example, the emergent behavior of the
robot described in the Unmanned Ground Vehicle competition in Sec. 5.4
could be described as an abstract “follow-path” behavior. Recall that the
robot’s program assumed that it started facing the line. A more general pur-
pose, reusable follow-path behavior would need to handle a broader range
of starting conditions, such as starting facing a bale or not perfectly lined up
IMPRINTING with the line. Another common initialization behavior is imprinting, where
the robot is presented with an object and then records the perceived color (or
other attribute) of the object for use with the nominal behavior. In the Pick
Up the Trash competitions, several teams literally showed the robot the Coke
can and let it determine the best values of “red” for the current lighting con-
ditions. Likewise, some abstract behaviors would need special termination
behavior. In the case of the UGR competition, the termination behaviors was
NULL, but it could have been the victory dance.
Third, some times robots fail in their task; these events are often called
EXCEPTIONS exceptions. An exception might be when the robot does not pick up a soda
can in over 10 minutes. Another behavior can be substituted (do a raster scan
rather than a random wander) or alternative set of parameters (use different
values for red).

5.5.5 Scripts

SCRIPTS Abstract behaviors often use scripts, 49;50;87;100 or a related construct called
SKILLS skills, 53;54 to create generic templates of assemblages of behaviors. Scripts
provide a different way of generating the logic for an assemblage of behav-