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Forward Chaining in Prolog

Forward Chaining in Prolog. FC Core. % add(P) adds P to DB and triggers forward chaining rules. add(P) :- clause(P,true), !. add(P) :- dbug("Adding ~p.~n",[P]), assert(P), foreach(ifAdded(P,Actions), call(Actions)). % remove(P) removes P from DB, triggering ifRemoved rules.

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Forward Chaining in Prolog

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  1. Forward Chainingin Prolog

  2. FC Core % add(P) adds P to DB and triggers forward chaining rules. add(P) :- clause(P,true), !. add(P) :- dbug("Adding ~p.~n",[P]), assert(P), foreach(ifAdded(P,Actions), call(Actions)). % remove(P) removes P from DB, triggering ifRemoved rules. remove(P) :- dbug("Removing ~p.~n",[P]), retract(P), foreach(ifRemoved(P,Actions), call(Actions)).

  3. Mapping rules into triggers % A=>B adds forward chaining rule to execute B whenever the facts % in A have all been added to the DB. % LHS is a conjunction ((P1,P2)=>Q) :- !, (P1=>(P2=>Q)). % LHS is a disjunction ((P1;P2)=>Q) :- !, (P1=>Q), (P2=>Q). % LHS is atomic. trigger already in DB? (P=>Q) :- ifAdded(P,Q), !. % LHS is atomic. Add trigger to DB (P=>Q) :- assert(ifAdded(P,Q)), foreach(clause(P,true),fcDo(Q)).

  4. If-removed rules % A=/>B adds ifRemoved rule to execute B whenever the % assertions in A have all been removed from the database. ((P1,P2)=/>Q) :- !, (P1=/>(P2=/>Q)). ((P1;P2)=/>Q) :- !, (P1=/>Q), (P2=/>Q). (P=/>Q) :- assert(ifRemoved(P,Q)). (=>X) :- add(X).

  5. A test file % FCTEST :- spouse(P1,P2) => add(spouse(P2,P1)). :- spouse(P1,P2) =/> remove(spouse(P2,P1)). :- => spouse(adam,eve)). :- spouse(X,Y), female(X) => add(wife(X,Y)). :- => female(eve). :- female(X), male(X) => add(contradiction(female(X), male(X))). :- contradiction(P,Q) => format(“CONTRADICTION: ~w and ~w.\n”, [P,Q]).

  6. | ?- [fctest]. Adding spouse(adam,eve). Adding spouse(eve,adam). yes | ?- listing(ifAdded). ifAdded(spouse(A,B), add(spouse(B,A))). ifAdded(a(A), (b(A),c(A)=>add(d(A)))). yes | ?- add(b(1)). Adding b(1). yes | ?- add(a(1)). Adding a(1). yes | ?- listing(ifAdded). ifAdded(spouse(A,B), add(spouse(B,A))). ifAdded(a(A), (b(A),c(A)=>add(d(A)))). ifAdded(b(1), (c(1)=>add(d(1)))). ifAdded(c(1), add(d(1))). yes | ?- add(c(1)). Adding c(1). Adding d(1). Yes | ?- b(X) => add(foo(X)), add(bar(X)). Adding foo(1). Adding bar(1). yes | ?- listing(ifAdded). ifAdded(spouse(A,B), add(spouse(B,A))). ifAdded(a(A), (b(A),c(A)=>add(d(A)))). ifAdded(b(1), (c(1)=>add(d(1)))). ifAdded(c(1), add(d(1))). ifAdded(b(A), (add(foo(A)),add(bar(A)))). yes Fc in action

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