org.dllearner.learningproblems.EvaluationCache.java Source code

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Here is the source code for org.dllearner.learningproblems.EvaluationCache.java

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/**
 * Copyright (C) 2007 - 2016, Jens Lehmann
 *
 * This file is part of DL-Learner.
 *
 * DL-Learner is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * DL-Learner is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.dllearner.learningproblems;

import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeMap;

import org.dllearner.utilities.datastructures.SortedSetTuple;
import org.semanticweb.owlapi.model.OWLClassExpression;
import org.semanticweb.owlapi.model.OWLIndividual;
import org.semanticweb.owlapi.model.OWLObjectIntersectionOf;
import org.semanticweb.owlapi.model.OWLObjectUnionOf;

import com.google.common.collect.Sets;

/**
 * Caches results of previous concept evaluation to speed up
 * further evaluations. Implements a fast evaluation approach,
 * which tries to infer the covered examples of a given concept
 * from previous results.
 * 
 * TODO Under construction.
 * @author Jens Lehmann
 *
 */
public class EvaluationCache {

    // maps a concept to a list of individuals it covers
    private Map<OWLClassExpression, SortedSet<OWLIndividual>> cache;
    private boolean checkForEqualConcepts = false;

    private SortedSet<OWLIndividual> examples;

    public EvaluationCache(SortedSet<OWLIndividual> examples) {
        this.examples = examples;
        cache = new TreeMap<>();
    }

    public void put(OWLClassExpression concept, SortedSet<OWLIndividual> individuals) {
        cache.put(concept, individuals);
    }

    /**
     * Determines which examples are instances of a concept.
     * @param concept the concept
     * @return A tuple of two sets, where the first element is the
     * set of individuals belonging to the class and the second element
     * is the set of individuals not belonging to the class. For all
     * elements, which are in neither of the sets, the cache cannot
     * safely determine whether they are concept instances or not.
     */
    public SortedSetTuple<OWLIndividual> infer(OWLClassExpression concept) {
        if (checkForEqualConcepts) {
            Set<OWLIndividual> pos = cache.get(concept);
            Set<OWLIndividual> neg = Sets.difference(examples, pos);
            return new SortedSetTuple<>(pos, neg);
        } else {
            // for a negation NOT C we can only say which concepts are not in it
            // (those in C), but we cannot say which ones are in NOT C

            // for a conjunction we know that the intersection of instances
            // of all children belongs to the concept
            if (concept instanceof OWLObjectIntersectionOf) {
                handleMultiConjunction((OWLObjectIntersectionOf) concept);
                // disjunctions are similar to conjunctions but we use union here;
                // note that there can be instances which are neither in a concept
                // C nor in a concept D, but in (C OR D)
            } else if (concept instanceof OWLObjectUnionOf) {
                List<OWLClassExpression> operands = ((OWLObjectUnionOf) concept).getOperandsAsList();
                Set<OWLIndividual> pos = cache.get(operands.get(0));
                for (int i = 1; i < operands.size(); i++) {
                    pos = Sets.union(pos, cache.get(operands.get(i)));
                }
                // in all other cases we cannot infer anything, so we return an
                // empty tuple
            } else {
                return new SortedSetTuple<>();
            }
        }

        return null;
    }

    private SortedSetTuple<OWLIndividual> handleMultiConjunction(OWLObjectIntersectionOf mc) {
        List<OWLClassExpression> operands = mc.getOperandsAsList();
        Set<OWLIndividual> pos = cache.get(operands.get(0));
        for (int i = 1; i < operands.size(); i++) {
            pos = Sets.intersection(pos, cache.get(operands.get(i)));
        }
        // TODO: handle the case that some children may not be in cache
        return null;
    }
}