source: trunk/EventBenchCore/src/de/ugoe/cs/eventbench/coverage/CoverageCalculator.java @ 114

package de.ugoe.cs.eventbench.coverage;

import java.security.InvalidParameterException;
import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;

import de.ugoe.cs.eventbench.data.Event;
import de.ugoe.cs.eventbench.models.IStochasticProcess;

/**
 * <p>
 * This class calculates various types of sequence coverage.
 * </p>
 * 
 * @author Steffen Herbold
 * @version 1.0
 */
public class CoverageCalculator {

        /**
         * <p>
         * Stochastic process that is the foundation for probabilistic coverages and
         * coverages with reference to all possible sequences.
         * </p>
         */
        private final IStochasticProcess process;

        /**
         * <p>
         * Sequences for which the coverage is calculated.
         * </p>
         */
        private final Collection<List<? extends Event<?>>> sequences;

        /**
         * <p>
         * Length of the subsequences in relation to which the covarage is
         * calculated.
         * </p>
         */
        private final int length;

        /**
         * <p>
         * All subsequences of {@link #length} of {@link #sequences}.
         * </p>
         */
        private Collection<List<? extends Event<?>>> containedSubSeqs = null;

        /**
         * <p>
         * All subsequences of {@link #length} that can be generated by
         * {@link #process}.
         * </p>
         */
        private Collection<List<? extends Event<?>>> allPossibleSubSeqs = null;

        /**
         * <p>
         * The probabilities of al subsequences of {@link #length} according to
         * {@link #process}.
         * </p>
         */
        private Map<List<? extends Event<?>>, Double> subSeqWeights = null;

        /**
         * <p>
         * Constructor. Creates a new CoverageCalculator for a given stochastic
         * process and generated sequences.
         * </p>
         * 
         * @param process
         *            stochastic process used for coverage calculations; must not be null
         * @param sequences
         *            sequences for which the coverage is calculated; must not be
         *            null
         * @param length
         *            length of the subsequences for which the coverage is analyzed;
         *            must be >0
         */
        public CoverageCalculator(IStochasticProcess process,
                        Collection<List<? extends Event<?>>> sequences, int length) {
                if( process==null ) {
                        throw new InvalidParameterException("process must not be null");
                }
                if( sequences==null ) {
                        throw new InvalidParameterException("sequences must not be null");
                }
                if( length<=0 ) {
                        throw new InvalidParameterException("length must be >0; actual value: " + length);
                }
                this.process = process;
                this.sequences = sequences;
                this.length = length;
        }

        /**
         * <p>
         * Calculates the percentage of subsequences of length k that exist occur,
         * including those that cannot be generated by {@link #process}.
         * </p>
         * 
         * @return coverage percentage
         */
        public double getCoverageAllNoWeight() {
                if (containedSubSeqs == null) {
                        containedSubSeqs = containedSubSequences(sequences, length);
                }
                return ((double) containedSubSeqs.size())
                                / numSequences(process, length);
        }

        /**
         * <p>
         * Calculates the percentage of subsequences of length k that occur and can
         * generated by {@link #process}.
         * </p>
         * 
         * @return coverage percentage
         */
        public double getCoveragePossibleNoWeight() {
                if (containedSubSeqs == null) {
                        containedSubSeqs = containedSubSequences(sequences, length);
                }
                if (allPossibleSubSeqs == null) {
                        allPossibleSubSeqs = process.generateSequences(length);
                }
                return ((double) containedSubSeqs.size()) / allPossibleSubSeqs.size();
        }

        /**
         * <p>
         * Calculates the weight of the subsequences that occur with relation to
         * {@link #process}, i.e., the mass of the subsequence probability covered
         * by the subsequences.
         * </p>
         * 
         * @return coverage weight
         */
        public double getCoveragePossibleWeight() {
                if (containedSubSeqs == null) {
                        containedSubSeqs = containedSubSequences(sequences, length);
                }
                if (allPossibleSubSeqs == null) {
                        allPossibleSubSeqs = process.generateSequences(length);
                }
                if (subSeqWeights == null) {
                        subSeqWeights = generateWeights(process, allPossibleSubSeqs);
                }
                double weight = 0.0;
                for (List<? extends Event<?>> subSeq : containedSubSeqs) {
                        weight += subSeqWeights.get(subSeq);
                }
                return weight;
        }

        /**
         * <p>
         * Calculates the weights for all sequences passed to this function as
         * defined by the stochastic process and stores them in a {@link Map}.
         * </p>
         * 
         * @param process
         *            process used for weight calculation
         * @param sequences
         *            sequences for which the weights are calculated
         * @return {@link Map} of weights
         */
        private static Map<List<? extends Event<?>>, Double> generateWeights(
                        IStochasticProcess process,
                        Collection<List<? extends Event<?>>> sequences) {
                Map<List<? extends Event<?>>, Double> subSeqWeights = new LinkedHashMap<List<? extends Event<?>>, Double>();
                double sum = 0.0;
                for (List<? extends Event<?>> sequence : sequences) {
                        double prob = 1.0;
                        List<Event<?>> context = new LinkedList<Event<?>>();
                        for (Event<?> event : sequence) {
                                prob *= process.getProbability(context, event);
                                context.add(event);
                        }
                        subSeqWeights.put(sequence, prob);
                        sum += prob;
                }
                if (sum < 1.0) {
                        for (Map.Entry<List<? extends Event<?>>, Double> entry : subSeqWeights
                                        .entrySet()) {
                                entry.setValue(entry.getValue() / sum);
                        }
                }
                return subSeqWeights;
        }

        /**
         * <p>
         * Calculates the number of all existing sequences of a given length,
         * regardless whether they are possible or not.
         * </p>
         * 
         * @param process
         *            stochastic process whose symbols are the basis for this
         *            calculation
         * @param length
         *            lenght of the sequences
         * @return numStates^length
         */
        private static long numSequences(IStochasticProcess process, int length) {
                return (long) Math.pow(process.getNumStates(), length);
        }

        /**
         * <p>
         * Creates a {@link Set} of all subsequences of a given length that are
         * contained in a sequence collection.
         * </p>
         * 
         * @param sequences
         *            sequences from which the subsequences are extracted
         * @param length
         *            length of the subsequences
         * @return {@link Set} of all subsequences
         */
        private static Set<List<? extends Event<?>>> containedSubSequences(
                        Collection<List<? extends Event<?>>> sequences, int length) {
                Set<List<? extends Event<?>>> containedSubSeqs = new LinkedHashSet<List<? extends Event<?>>>();
                for (List<? extends Event<?>> sequence : sequences) {
                        List<Event<?>> subSeq = new LinkedList<Event<?>>();
                        boolean minLengthReached = false;
                        for (Event<?> event : sequence) {
                                subSeq.add(event);
                                if (!minLengthReached) {
                                        if (subSeq.size() == length) {
                                                minLengthReached = true;
                                        }
                                } else {
                                        subSeq.remove(0);
                                }
                                if (minLengthReached) {
                                        if (!containedSubSeqs.contains(subSeq)) {
                                                containedSubSeqs.add(new LinkedList<Event<?>>(subSeq));
                                        }
                                }
                        }
                }
                return containedSubSeqs;
        }

}