Each model has zero or more properties associated with it; these
properties specify characteristics such as an object's shape or a
sensor's range. Models are organized into a heriarchy, with sub-types
inheriting properties from their parent type. All passive
environmental objects (boxes, pucks and bitmaps) are derived from a
entity type and are referred to as objects.
Similary, all sensors and actuator models are derived from a generic
device type, and referred to as devices. The
type is itself derived from
entity, so they devices inherit all
the standrd entity properties.
Note that both the
device types are abstract (in C++ parlance) since they cannot be instantiated