% -*-Prolog-*- %% a simple Pfc example - the one bulb problem (see DeKleer and %% Williams, IJCAI89) %% %% Tim Finin, finin@prc.unisys.com, 8/89 % a conflict triggers a Prolog action to resolve it. conflict(C) => {resolveConflict(C)}. % this isn't written yet. resolveConflict(C) :- format("~NHalting with conflict ~w", [C]), pfcHalt. % meta rules to schedule inferencing. % resolve conflicts asap pfcSelect(conflict(X)) :- pfcQueue(conflict(X)). % a pretty basic conflict. not(P), P => conflict(P). % Devices behave as intended unless they are faulty. isa(X,Class), ~faulty(X) => behave(X,Class). % assume an observation is true. observed(P), ~false_observation(P) => P. % connecting two terminals means their voltages are equal. con(T1,T2) => (volt(T1,V) <=> volt(T2,V)). % a wire behaves by connecting its two terminals. behave(X,wire) => con(t1(X),t2(X)). % a battery's behaviour behave(X,battery) => volt(t1(X),1.5), volt(t2(X),0). % a bulb's behaviour. behave(X,bulb), volt(t1(X),V1), volt(t2(X),V2), {V1\==V2} => lit(X). % It is a conflict if a terminal has two different voltages. % volt(T,V1), volt(T,V2)/(\+V1=:=V2) => conflict(two_voltages(T,V1,V2)). %% ***** here is a particular test case. ***** % here is a particular circuit - a gizmo. isa(X,gizmo) => isa(battery(X),battery), isa(bulb(X),bulb), isa(w1(X),wire), isa(w2(X),wire), con(t1(battery(X)),t1(w1(X))), con(t2(battery(X)),t1(w2(X))), con(t2(w1(X)),t1(bulb(X))), con(t2(bulb(X)),t2(w2(X))). %% here is a diagnostic problem for a gizmo. test(X) :- add([isa(X,gizmo), observed(not(lit(bulb(X))))]).