This example illustrates how Prolog object can be used in classification of certain concepts. This style is common in expert system application for describing its domain.
animal :: {
super(object) &
relative_size(S) :-
size(Obj_size),
super(Obj_prototype),
Obj_prototype :: size(Prototype_size),
:(S is Obj_size/Prototype_size * 100)
}.
bird :: {
super(animal) &
moving_method(fly) &
active_at(daylight)
}.
albatross :: {
super(bird) &
color(black_and_white) &
size(115)
}.
kiwi :: {
super(bird) &
moving_method(walk) &
active_at(night) &
size(40) &
color(brown)
}.
albert :: {
super(albatross) &
size(120)
}.
ross :: {
super(albatross) &
size(40)
}.
| ?- ross :: relative_size(R).
R = 34.78