public bool plfcEntails(KnowledgeBase kb, Symbol q)
{
List<HornClause> hornClauses = asHornClauses(kb.getSentences());
while (agenda.Count != 0)
{
Symbol p = agenda.Pop();
while (!inferred(p))
{
_inferred.Add(p, true);
for (int i = 0; i < hornClauses.Count; i++)
{
HornClause hornClause = hornClauses[i];
if (hornClause.premisesContainsSymbol(p))
{
decrementCount(hornClause);
if (countisZero(hornClause))
{
if (hornClause.head().Equals(q))
{
return true;
}
else
{
agenda.Push(hornClause.head());
}
}
}
}
}
}
return false;
}
public override Object visitSymbol(Symbol symbol, Object arg)
{
List<Symbol> s = (List<Symbol>)arg;
s.Add(symbol);// add ALL symbols not discarded by the visitNotSentence
// mathod
return arg;
}
public Model flip(Symbol s) {
if (isTrue(s)) {
return extend(s, false);
}
if (isFalse(s)) {
return extend(s, true);
}
return this;
}
public void testListOfSymbolsClone()
{
List<Symbol> l = new List<Symbol>();
l.Add(new Symbol("A"));
l.Add(new Symbol("B"));
l.Add(new Symbol("C"));
Symbol[] copy = new Symbol[l.Count];
l.CopyTo(copy);
List<Symbol> l2 = copy.ToList<Symbol>();
l2.Remove(new Symbol("B"));
Assert.AreEqual(3, l.Count);
Assert.AreEqual(2, l2.Count);
}
public Object visitSymbol(Symbol s, Object arg)
{
return new Symbol(s.getValue());
}
public override Object visitSymbol(Symbol s, Object arg)
{
List<Symbol> symbolsCollectedSoFar = (List<Symbol>)arg;
symbolsCollectedSoFar.Add(new Symbol(s.getValue()));
return symbolsCollectedSoFar;
}
//
// START-PLVisitor
public Object visitSymbol(Symbol s, Object arg) {
return getStatus(s);
}
public SymbolValuePair findPureSymbolValuePair(List<Sentence> clauseList,
Model model, List<Symbol> symbols)
{
List<Sentence> _clausesWithNonTrueValues = clausesWithNonTrueValues(clauseList,
model);
Sentence nonTrueClauses = LogicUtils.chainWith("AND",
_clausesWithNonTrueValues);
// System.Console.WriteLine("Unsatisfied clauses = "
// + clausesWithNonTrueValues.Count);
List<Symbol> symbolsAlreadyAssigned = new List<Symbol>( model.getAssignedSymbols());
// debug
// List symList = asList(symbolsAlreadyAssigned);
//
// System.Console.WriteLine(" assignedSymbols = " + symList.Count);
// if (symList.Count == 52) {
// System.Console.WriteLine("untrue clauses = " + clausesWithNonTrueValues);
// System.Console.WriteLine("model= " + model);
// }
// debug
List<Symbol> purePositiveSymbols = SetOps
.difference(new SymbolClassifier()
.getPurePositiveSymbolsIn(nonTrueClauses),
symbolsAlreadyAssigned);
List<Symbol> pureNegativeSymbols = SetOps
.difference(new SymbolClassifier()
.getPureNegativeSymbolsIn(nonTrueClauses),
symbolsAlreadyAssigned);
// if none found return "not found
if ((purePositiveSymbols.Count == 0)
&& (pureNegativeSymbols.Count == 0))
{
return new SymbolValuePair();// automatically set to null values
}
else
{
if (purePositiveSymbols.Count > 0)
{
Symbol symbol =purePositiveSymbols[0];
if (pureNegativeSymbols.Contains(symbol))
{
throw new ApplicationException("Symbol " + symbol.getValue()
+ "misclassified");
}
return new SymbolValuePair(symbol, true);
}
else
{
Symbol symbol = new Symbol((pureNegativeSymbols[0])
.getValue());
if (purePositiveSymbols.Contains(symbol))
{
throw new ApplicationException("Symbol " + symbol.getValue()
+ "misclassified");
}
return new SymbolValuePair(symbol, false);
}
}
}
public SymbolValuePair()
{
// represents "No Symbol found with a bool value that makes all
// its literals true
symbol = null;
}
public bool isTrue(Symbol symbol) {
return true.Equals(h[symbol]);
}
public bool getStatus(Symbol symbol) {
return h[symbol];
}
private bool inferred(Symbol p)
{
Object value = _inferred[p];
return ((value == null) || value.Equals(true));
}
public bool premisesContainsSymbol(Symbol q)
{
return premiseSymbols.Contains(q);
}
public HornClause(Sentence sentence, PLFCEntails plfcEntails)
{
this.plfcEntails = plfcEntails;
if (sentence is Symbol)
{
_head = (Symbol)sentence;
plfcEntails.agenda.Push(_head);
premiseSymbols = new List<Symbol>();
plfcEntails.count.Add(this, 0);
plfcEntails._inferred.Add(_head, false);
}
else if (!isImpliedSentence(sentence))
{
throw new ApplicationException("Sentence " + sentence
+ " is not a horn clause");
}
else
{
BinarySentence bs = (BinarySentence)sentence;
_head = (Symbol)bs.getSecond();
if (plfcEntails._inferred.ContainsKey(_head))
{
plfcEntails._inferred[_head] = false;
}
else
{
plfcEntails._inferred.Add(_head, false);
}
List<Symbol> symbolsInPremise = new SymbolCollector()
.getSymbolsIn(bs.getFirst());
foreach(Symbol s in symbolsInPremise)
{
plfcEntails._inferred.Add(s, false);
}
premiseSymbols = symbolsInPremise;
plfcEntails.count.Add(this, premiseSymbols.Count);
}
}
public Object visitSymbol(Symbol s, Object arg)
{
return false;
}
//
// PRIVATE METHODS
//
private bool dpll(List<Sentence> clauses, List<Symbol> symbols, Model model)
{
// List<Sentence> clauseList = asList(clauses);
List<Sentence> clauseList = clauses;
// System.Console.WriteLine("clauses are " + clauses.ToString());
// if all clauses are true return true;
if (areAllClausesTrue(model, clauseList))
{
// System.Console.WriteLine(model.ToString());
return true;
}
// if even one clause is false return false
if (isEvenOneClauseFalse(model, clauseList))
{
// System.Console.WriteLine(model.ToString());
return false;
}
// System.Console.WriteLine("At least one clause is unknown");
// try to find a unit clause
SymbolValuePair svp = findPureSymbolValuePair(clauseList, model,
symbols);
if (svp.notNull())
{
Symbol[] copy = new Symbol[symbols.Count];
symbols.CopyTo(copy);
List<Symbol> newSymbols = new List<Symbol>(copy);
newSymbols.Remove(new Symbol(svp.symbol.getValue()));
Model newModel = model.extend(new Symbol(svp.symbol.getValue()),
svp.value);
return dpll(clauses, newSymbols, newModel);
}
SymbolValuePair svp2 = findUnitClause(clauseList, model, symbols);
if (svp2.notNull())
{
Symbol[] copy = new Symbol[symbols.Count];
symbols.CopyTo(copy);
List<Symbol> newSymbols = new List<Symbol>(copy);
newSymbols.Remove(new Symbol(svp2.symbol.getValue()));
Model newModel = model.extend(new Symbol(svp2.symbol.getValue()),
svp2.value);
return dpll(clauses, newSymbols, newModel);
}
Symbol symbol = (Symbol)symbols[0];
// System.Console.WriteLine("default behaviour selecting " + symbol);
Symbol[] symbolsArr = new Symbol[symbols.Count];
symbols.CopyTo(symbolsArr);
List<Symbol> newSymbols2 = symbolsArr.ToList<Symbol>();
newSymbols2.RemoveAt(0);
return (dpll(clauses, newSymbols2, model.extend(symbol, true)) || dpll(
clauses, newSymbols2, model.extend(symbol, false)));
}
public bool isFalse(Symbol symbol) {
return false.Equals(h[symbol]);
}
public SymbolValuePair(Symbol symbol, bool b)
{
// represents "Symbol found with a bool value that makes all
// its literals true
this.symbol = symbol;
value = b;
}
public Model extend(Symbol symbol, bool b) {
Model m = new Model();
m.h = this.h;
m.h.Add(symbol, b);
return m;
}
public virtual Object visitSymbol(Symbol s, Object arg)
{
return arg;
}
private Sentence createResolventClause(ClauseSymbols cs, Symbol toRemove)
{
List<Symbol> positiveSymbols = SetOps
.union(cs.clause1PositiveSymbols, cs.clause2PositiveSymbols);
List<Symbol> negativeSymbols = SetOps
.union(cs.clause1NegativeSymbols, cs.clause2NegativeSymbols);
if (positiveSymbols.Contains(toRemove))
{
positiveSymbols.Remove(toRemove);
}
if (negativeSymbols.Contains(toRemove))
{
negativeSymbols.Remove(toRemove);
}
positiveSymbols.Sort(new SymbolComparator());
negativeSymbols.Sort( new SymbolComparator());
List<Sentence> sentences = new List<Sentence>();
for (int i = 0; i < positiveSymbols.Count; i++)
{
sentences.Add(positiveSymbols[i]);
}
for (int i = 0; i < negativeSymbols.Count; i++)
{
sentences.Add(new UnarySentence(negativeSymbols[i]));
}
if (sentences.Count == 0)
{
return new Symbol("EMPTY_CLAUSE"); // == empty clause
}
else
{
return LogicUtils.chainWith("OR", sentences);
}
}