public string Ask(Symbol query, KnowledgeBase kb)
{
_kb = kb;
_path = new List <string>();
if (kb.SymbolIsKnown(query))
{
return("YES: " + query.Name);
}
if (BackwardChain(query))
{
return("YES: " + PathString);
}
return("NO");
}
private bool BackwardChain(Symbol s)
{
_path.Insert(0, s.Name);
if (_kb.SymbolIsKnown(s))
{
return(true);
}
foreach (var symbol in GetSymbolsImplying(s))
{
if (!BackwardChain(symbol))
{
return(false);
}
}
return(true);
}
public string Ask(Symbol query, KnowledgeBase kb)
{
_kb = kb;
// count = Dictionary<string, int>
// Number of premises for each sentence
var count = new Dictionary <Sentence, int>();
foreach (var sentence in kb.Knowledge)
{
count[sentence] = sentence.LeftSide.Count;
}
// inferred = Dictionary<string, bool>
// Whether each symbol has been inferred yet
var inferred = new Dictionary <string, bool>();
foreach (var symbol in kb.Symbols)
{
inferred[symbol.Key] = false;
}
// agenda = List<Symbol>
// The inferred symbols. Begins with "known" symbols
var agenda = new Stack <Symbol>();
foreach (var symbol in kb.Symbols)
{
if (kb.SymbolIsKnown(symbol.Value))
{
agenda.Push(symbol.Value);
}
}
string path = "";
foreach (var symbol in agenda)
{
path += symbol.Name + " ";
}
while (agenda.Count > 0)
{
var premise = agenda.Pop();
if (!inferred[premise.Name])
{
inferred[premise.Name] = true;
foreach (var sentence in GetSentencesContaining(premise))
{
--count[sentence];
if (count[sentence] == 0)
{
if (sentence.Implication.Name == query.Name)
{
return("YES: " + path + query.Name);
}
agenda.Push(sentence.Implication);
path += sentence.Implication.Name + " ";
}
}
}
}
return(query.Name + ": NO");
}
