org.coode.oppl.similarity.SymbolBasedSimilarity Maven / Gradle / Ivy

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package org.coode.oppl.similarity;

import static org.coode.oppl.utils.ArgCheck.checkNotNull;

import java.util.Collection;
import java.util.HashSet;
import java.util.Set;

import org.coode.oppl.utils.OWLObjectExtractor;
import org.semanticweb.owlapi.model.OWLObject;

/** Compares OWLObject instances only based on the symbols they contain.
 * 
 * @author Luigi Iannone */
public class SymbolBasedSimilarity implements SimilarityMeasure {
    @Override
    public double compare(OWLObject anObject, OWLObject anotherObject) {
        Set anObjectOWLPrimitives = extractSymbols(checkNotNull(anObject,
                "anObject"));
        Set anotherObjectOWLPrimitives = extractSymbols(checkNotNull(
                anotherObject, "anotherObject"));
        return compareSymbols(anObjectOWLPrimitives, anotherObjectOWLPrimitives);
    }

    /** Compares symbols computing the ratio of the size of their intersection
     * over the size of their union. Users may override this for different
     * comparison strategies.
     * 
     * @param anObjectSymbols
     *            First Collection of Symbols. Cannot be {@code null}.
     * @param anotherObjectSymbols
     *            Second Collection of Symbols. Cannot be {@code null}.
     * @throws NullPointerException
     *             when either input is {@code null}.
     * @return the double representing the result of the comparison. */
    protected double compareSymbols(Collection anObjectSymbols,
            Collection anotherObjectSymbols) {
        checkNotNull(anObjectSymbols, "anObjectSymbols");
        checkNotNull(anotherObjectSymbols, "anotherObjectSymbols");
        // If both collection are empty 0 the method wil return 0
        double toReturn = anObjectSymbols.isEmpty() && anotherObjectSymbols.isEmpty() ? 0
                : 1;
        if (toReturn > 0) {
            Set intersection = new HashSet(anObjectSymbols);
            intersection.retainAll(anotherObjectSymbols);
            Set union = new HashSet(anObjectSymbols);
            union.addAll(anotherObjectSymbols);
            toReturn = (double) intersection.size() / (double) union.size();
        }
        return toReturn;
    }

    /** Extracts the relevant symbols for the comparison. Override this when a
     * different set of symbols from the all the OWLEntity and OWLConstant
     * appearing the input object should be used.
     * 
     * @param anObject
     *            The OWLObject from which the symbols should be extracted.
     *            Cannot be {@code null}.
     * @return a Set containing the OWL Object (symbols) that can be used for
     *         the comparison. 1 corresponds to maximum similarity, 0 to
     *         minimal.
     * @throws NullPointerException
     *             when the input is {@code null}. */
    protected Set extractSymbols(OWLObject anObject) {
        return OWLObjectExtractor.getAllOWLPrimitives(checkNotNull(anObject, "anObject"));
    }

    @Override
    public boolean isSymmetric() {
        return true;
    }
}