public InferenceResult ask(FOLKnowledgeBase kb, Sentence query)
{
//
// Get the background knowledge - are assuming this is satisfiable
// as using Set of Support strategy.
ISet <Clause> bgClauses = CollectionFactory.CreateSet <Clause>(kb.getAllClauses());
bgClauses.RemoveAll(SubsumptionElimination.findSubsumedClauses(bgClauses));
ICollection <Chain> background = createChainsFromClauses(bgClauses);
// Collect the information necessary for constructing
// an answer (supports use of answer literals).
AnswerHandler ansHandler = new AnswerHandler(kb, query, maxQueryTime, this);
IndexedFarParents 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())
{
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 = false;
bool dropped = false;
do
{
cancelled = false;
Chain nextParent = null;
while (nextNearParent != (nextParent = tryCancellation(nextNearParent)))
{
nextNearParent = nextParent;
cancelled = true;
}
dropped = false;
while (nextNearParent != (nextParent = 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
recursiveDLS(maxDepth, currentDepth + 1, nextNearParent,
indexedFarParents, ansHandler);
// Reset the number of far parents possible
// when recursing back up.
indexedFarParents.resetNumberFarParentsTo(nextNearParent,
noNextFarParents);
}
}
}