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package uk.ac.ox.cs.pagoda.rules;
import org.semanticweb.HermiT.model.DLClause;
import uk.ac.ox.cs.pagoda.multistage.AnswerTupleID;
import java.util.*;
/**
* Approximates existential rules by a limited form of Skolemisation.
* <p>
* Given a rule and a grounding substitution,
* it Skolemises the rule if
* all the terms in the substitution have depth less than a given depth,
* otherwise it approximates using an alternative <tt>TupleDependentApproximator</tt>.
*
* */
public class LimitedSkolemisationApproximator implements TupleDependentApproximator {
private final int maxTermDepth;
private final TupleDependentApproximator alternativeApproximator;
private Map<AnswerTupleID, Integer> mapIndividualsToDepth;
public LimitedSkolemisationApproximator(int maxTermDepth) {
this(maxTermDepth, new ExistConstantApproximator());
}
public LimitedSkolemisationApproximator(int maxTermDepth, TupleDependentApproximator alternativeApproximator) {
this.maxTermDepth = maxTermDepth;
this.alternativeApproximator = alternativeApproximator;
this.mapIndividualsToDepth = new HashMap<>();
}
@Override
public Collection<DLClause> convert(DLClause clause, DLClause originalClause, Collection<AnswerTupleID> violationTuples) {
switch (clause.getHeadLength()) {
case 1:
return overApprox(clause, originalClause, violationTuples);
case 0:
return Arrays.asList(clause);
default:
ArrayList<DLClause> result = new ArrayList<>();
// TODO implement
return result;
}
}
private Collection<DLClause> overApprox(DLClause clause, DLClause originalClause, Collection<AnswerTupleID> violationTuples) {
ArrayList<DLClause> result = new ArrayList<>();
for (AnswerTupleID violationTuple : violationTuples)
if (getDepth(violationTuple) > maxTermDepth)
result.addAll(alternativeApproximator.convert(clause, originalClause, null));
else
result.add(getInstantiatedSkolemisation(clause, originalClause, violationTuple));
return result;
}
private DLClause getInstantiatedSkolemisation(DLClause clause, DLClause originalClause, AnswerTupleID violationTuple) {
// TODO implement
return null;
}
private int getDepth(AnswerTupleID violationTuple) {
if (!mapIndividualsToDepth.containsKey(violationTuple)) return 0;
return mapIndividualsToDepth.get(violationTuple);
}
}
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