/*
* ARX: Powerful Data Anonymization
* Copyright 2012 - 2017 Fabian Prasser, Florian Kohlmayer and contributors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.deidentifier.arx.algorithm;
import java.util.Comparator;
import java.util.PriorityQueue;
import org.deidentifier.arx.framework.check.NodeChecker;
import org.deidentifier.arx.framework.check.history.History.StorageStrategy;
import org.deidentifier.arx.framework.lattice.SolutionSpace;
import org.deidentifier.arx.framework.lattice.Transformation;
import cern.colt.list.LongArrayList;
import de.linearbits.jhpl.PredictiveProperty;
/**
*
* @author Fabian Prasser
* @author Raffael Bild
* @author Johanna Eicher
* @author Helmut Spengler
*/
public class LIGHTNINGAlgorithm extends AbstractAlgorithm{
/**
* Creates a new instance
* @param solutionSpace
* @param checker
* @param timeLimit
* @return
*/
public static AbstractAlgorithm create(SolutionSpace solutionSpace,
NodeChecker checker,
int timeLimit) {
return new LIGHTNINGAlgorithm(solutionSpace, checker, timeLimit);
}
/** Property */
private final PredictiveProperty propertyChecked;
/** Property */
private final PredictiveProperty propertyExpanded;
/** The number indicating how often a depth-first-search will be performed */
private final int stepping;
/** Time limit */
private final int timeLimit;
/** The start time */
private long timeStart;
/**
* Constructor
* @param space
* @param checker
* @param timeLimit
*/
private LIGHTNINGAlgorithm(SolutionSpace space, NodeChecker checker, int timeLimit) {
super(space, checker);
this.checker.getHistory().setStorageStrategy(StorageStrategy.ALL);
int stepping = space.getTop().getLevel();
this.stepping = stepping > 0 ? stepping : 1;
this.propertyChecked = space.getPropertyChecked();
this.propertyExpanded = space.getPropertyExpanded();
this.solutionSpace.setAnonymityPropertyPredictable(false);
this.timeLimit = timeLimit;
if (timeLimit <= 0) {
throw new IllegalArgumentException("Invalid time limit. Must be greater than zero.");
}
}
@Override
public void traverse() {
timeStart = System.currentTimeMillis();
PriorityQueue<Long> queue = new PriorityQueue<Long>(stepping, new Comparator<Long>() {
@Override
public int compare(Long arg0, Long arg1) {
return solutionSpace.getUtility(arg0).compareTo(solutionSpace.getUtility(arg1));
}
});
Transformation bottom = solutionSpace.getBottom();
assureChecked(bottom);
queue.add(bottom.getIdentifier());
Transformation next;
int step = 0;
Long nextId;
while ((nextId = queue.poll()) != null) {
next = solutionSpace.getTransformation(nextId);
if (!prune(next)) {
step++;
if (step % stepping == 0) {
dfs(queue, next);
} else {
expand(queue, next);
}
if (getTime() > timeLimit) {
return;
}
}
}
}
/**
* Makes sure that the given Transformation has been checked
* @param transformation
*/
private void assureChecked(final Transformation transformation) {
if (!transformation.hasProperty(propertyChecked)) {
transformation.setChecked(checker.check(transformation, true));
trackOptimum(transformation);
progress((double)(System.currentTimeMillis() - timeStart) / (double)timeLimit);
}
}
/**
* Performs a depth first search (without backtracking) starting from the the given transformation
* @param queue
* @param transformation
*/
private void dfs(PriorityQueue<Long> queue, Transformation transformation) {
if (getTime() > timeLimit) {
return;
}
Transformation next = expand(queue, transformation);
if (next != null) {
queue.remove(next);
dfs(queue, next);
}
}
/**
* Returns the successor with minimal information loss, if any, null otherwise.
* @param queue
* @param transformation
* @return
*/
private Transformation expand(PriorityQueue<Long> queue, Transformation transformation) {
Transformation result = null;
LongArrayList list = transformation.getSuccessors();
for (int i = 0; i < list.size(); i++) {
long id = list.getQuick(i);
Transformation successor = solutionSpace.getTransformation(id);
if (!successor.hasProperty(propertyExpanded)) {
assureChecked(successor);
queue.add(successor.getIdentifier());
if (result == null || successor.getInformationLoss().compareTo(result.getInformationLoss()) < 0) {
result = successor;
}
}
if (getTime() > timeLimit) {
return null;
}
}
transformation.setProperty(propertyExpanded);
return result;
}
/**
* Returns the current execution time
* @return
*/
private int getTime() {
return (int)(System.currentTimeMillis() - timeStart);
}
/**
* Returns whether we can prune this Transformation
* @param transformation
* @return
*/
private boolean prune(Transformation transformation) {
// Depending on monotony of metric we choose to compare either IL or monotonic subset with the global optimum
boolean prune = false;
if (getGlobalOptimum() != null) {
// A Transformation (and it's direct and indirect successors, respectively) can be pruned if
// the information loss is monotonic and the nodes's IL is greater or equal than the IL of the
// global maximum (regardless of the anonymity criterion's monotonicity)
// TODO: We could use this for predictive tagging as well!
if (checker.getMetric().isMonotonic(checker.getConfiguration().getMaxOutliers())) {
prune = transformation.getLowerBound().compareTo(getGlobalOptimum().getInformationLoss()) >= 0;
}
}
return (prune || transformation.hasProperty(propertyExpanded));
}
}