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5.2 Behaviors as Objects in OOP
It is better software engineering to write a general move to goal behavior,
where only what is the goal—a red region or a blue region—varies. The goal
for the current instance can be passed in at instantiation through the object
constructor.
Writing a single generic behavior for move_to_goal(color) is more
desirable than writing a move_to_red and a move_to_blue behaviors.
From a software engineering perspective, writing two behaviors which do
the same thing is an opportunity to introduce a programming bug in one
of them and not notice because they are supposed to be the same. Generic
behaviors also share the same philosophy as factoring in mathematics. Con-
2
sider simplifying the equation 45 x + x + . The first step is to fact 9or out 0 5
4
any common term to simplify the equation. In this case, 45 can be factored
and the equation rewritten as 45( x + 2 . The color of the goal, red or 1blue, )
was like the common coefficient of 45; it is important, but tends to hide that
the key to the solution was the move-to-goal part, or x.
Modular, generic code can be handled nicely by schemas as shown in
Fig. 5.2. The behavior move_to_goal would consist of a perceptual schema,
which will be called extract-goal, and a motor schema, which uses an
attractive field called pfields.attraction. extract-goal uses the af-
fordance of color to extract where the goal is in the image, and then computes
the angle to the center of the colored region and the size of the region. This
AFFORDANCE information forms the percept of the goal; the affordance of the Coke can is
the color, while the information extracted from the perception is the angle
and size. The attraction motor schema takes that percept and is responsible
for using it to turn the robot to center on the region and move forward. It
can do this easily by using an attractive field, where the larger the region, the
stronger the attraction and the faster the robot moves.
The move_to_goal behavior can be implemented as a primitive behavior,
where goal_color is a numerical means of representing different colors
such as red and blue:

move_to_goal(goal_color):
Object Behavioral Analog Identifier
Data percept goal_angle
goal_strength
Methods perceptual_schema extract_goal(goal_color)
motor_schema pfields.attraction(goal_angle, goal_strength)

The above table implies some very important points about programming
with behaviors: