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