public IInferenceResult Ask(FOLKnowledgeBase kb, ISentence aQuery)
{
//
// Get the background knowledge - are assuming this is satisfiable
// as using Set of Support strategy.
ISet <Clause> bgClauses = new HashedSet <Clause>(kb.GetAllClauses());
bgClauses.ExceptWith(SubsumptionElimination.FindSubsumedClauses(bgClauses));
IList <Chain> background = CreateChainsFromClauses(bgClauses);
// Collect the information necessary for constructing
// an answer (supports use of answer literals).
var ansHandler = new AnswerHandler(kb, aQuery, this.MaxQueryTime);
var ifps = new IndexedFarParents(ansHandler
.GetSetOfSupport(), background);
// Iterative deepening to be used
for (int maxDepth = 1; maxDepth < int.MaxValue; maxDepth++)
{
// Track the depth actually reached
ansHandler.ResetMaxDepthReached();
if (null != tracer)
{
tracer.Reset();
}
foreach (Chain nearParent in ansHandler.GetSetOfSupport())
{
this.RecursiveDls(maxDepth, 0, nearParent, ifps, ansHandler);
if (ansHandler.IsComplete())
{
return(ansHandler);
}
}
// This means the search tree
// has bottomed out (i.e. finite).
// Return what I know based on exploring everything.
if (ansHandler.GetMaxDepthReached() < maxDepth)
{
return(ansHandler);
}
}
return(ansHandler);
}
// Recursive Depth Limited Search
private void RecursiveDls(int maxDepth, int currentDepth, Chain nearParent,
IndexedFarParents indexedFarParents, AnswerHandler ansHandler)
{
// Keep track of the maximum depth reached.
ansHandler.UpdateMaxDepthReached(currentDepth);
if (currentDepth == maxDepth)
{
return;
}
int noCandidateFarParents = indexedFarParents
.GetNumberCandidateFarParents(nearParent);
if (null != tracer)
{
tracer.Increment(currentDepth, noCandidateFarParents);
}
indexedFarParents.StandardizeApart(nearParent);
for (int farParentIdx = 0; farParentIdx < noCandidateFarParents; farParentIdx++)
{
// If have a complete answer, don't keep
// checking candidate far parents
if (ansHandler.IsComplete())
{
break;
}
// Reduction
Chain nextNearParent = indexedFarParents.AttemptReduction(
nearParent, farParentIdx);
if (null == nextNearParent)
{
// Unable to remove the head via reduction
continue;
}
// Handle Canceling and Dropping
bool cancelled;
bool dropped;
do
{
cancelled = false;
Chain nextParent;
while (nextNearParent != (nextParent = this.TryCancellation(nextNearParent)))
{
nextNearParent = nextParent;
cancelled = true;
}
dropped = false;
while (nextNearParent != (nextParent = this.TryDropping(nextNearParent)))
{
nextNearParent = nextParent;
dropped = true;
}
} while (dropped || cancelled);
// Check if have answer before
// going to the next level
if (!ansHandler.IsAnswer(nextNearParent))
{
// Keep track of the current # of
// far parents that are possible for the next near parent.
int noNextFarParents = indexedFarParents
.GetNumberFarParents(nextNearParent);
// Add to indexed far parents
nextNearParent = indexedFarParents.AddToIndex(nextNearParent);
// Check the next level
this.RecursiveDls(maxDepth, currentDepth + 1, nextNearParent,
indexedFarParents, ansHandler);
// Reset the number of far parents possible
// when recursing back up.
indexedFarParents.ResetNumberFarParentsTo(nextNearParent,
noNextFarParents);
}
}
}
