%% Top-Down Execution of Programs

% Schema
%-------
database({part(Number:integer, Shape:any, Weight:any)}).

%A DB of flat parts described by their geometric shape and weight.
%Different geometric shapes require a different number of
%parameters. Also actualkg is the actual weight of the
%part, but  unitkg is the specific weight where the actual
%weight can be easily derived from the area of the part

part_weight(No, Kilos) <- part(No, _, actualkg(Kilos)).
part_weight(No, Kilos) <- part(No, Shape, unitkg(K)),
			  area(Shape, A),
			  Kilos = K * A.

% functor
area(circle(Dmtr), A1) <- A1 = Dmtr * Dmtr * 3.14/4.
area(rectangle(Base, Height), A1) <- A1 = Base*Height.

export part_weight(X, Y).

% we may also reversely derive unitkg from actualkg and area
unit_weight(No, Kilos) <- part(No, Shape, actualkg(K)),
			  area(Shape, A),
			  Kilos = K / A.

export unit_weight(X, Y).