The SICStus Objects system implements a default inheritance mechanism.
By declaring within an object which objects are super-objects, the
hierarchy of objects are maintained. The system also maintains for each
object its immediate sub-objects (i.e. immediate children). Each
object may also call Prolog predicates. At the top of the
hierarchy, the proto-object object provides various services for
other objects. If object is not used at the top of the hierarchy
many services will not be available for other objects (check what
methods are available in object by sending the message
method/1 to object).