object(supermarket). % objects in figure 1.6
object(check_out_till_line).
object(check_out_station).
class(shop). % classes and objects used
object(shelving_aisles). % implicitly
object(freezer_banks).
object(trolley_parks).
object(supermarket).
% -- define frame for SUPERMARKET --
slot(supermarket,instance_of,shop).
slot(supermarket,location,out_of_town).
slot(supermarket,comprises,[check_out_till_line,shelving_aisles,freezer_banks]).
% -- define frame for CHECK-OUT TILL LINE --
slot(check_out_till_line,location,supermarket_exit).
slot(check_out_till_line,number,50).
slot(check_out_till_line,comprises,[check_out_station,trolley_parks]).
% RUNNING THIS CODE
%
% Actually very little you can do with the above except examine
% specific facts.
% However, this can be combined with the sort of code you saw
% in the semantic network to give inheritance etc.
%
% For example, we might have a default location for a shop
slot(shop,location,town_centre).
% and other kinds of shop:
object(veras_veggies).
slot(veras_veggies,instance_of,shop).
slot(veras_veggies,sells,vegetables).
% Inheritance rules can then be written using the 'instance_of' slot:
has_slot(OC,P,V) :- slot(OC,P,V).
has_slot(O,P,V) :- \+ slot(O,P,V),
slot(O,instance_of,C),
has_slot(C,P,V).
has_slot(C1,P,V) :- \+ slot(C1,P,V),
slot(C1,is_a,C2), % assume that classes may have
has_slot(C2,P,V). % an 'is-a' slot
% Now you can ask questions about shop locations:
%
%> has_slot(veras_veggies,location,X).
%
%> has_slot(supermarket,location,X).
%
% The former will give the answer 'town_centre' using the inherited
% default location from 'shop. However, the latter should give the
% answer 'out_of_town' as the supermarket's own slot overrides the
% shop slot.
%
% EXAMPLES
%
%> has_slot(veras_veggies,location,X). % default shop location 'town_centre'
%
%> has_slot(supermarket,location,X). % supermarket overrides location as 'out_of_town'
