it.unitn.disi.smatch.matchers.element.string.NGram Maven / Gradle / Ivy

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A version of S-Match semantic matching framework for Open Data
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package it.unitn.disi.smatch.matchers.element.string;

import it.unitn.disi.common.components.Configurable;
import it.unitn.disi.common.components.ConfigurableException;
import it.unitn.disi.smatch.data.mappings.IMappingElement;
import it.unitn.disi.smatch.matchers.element.IStringBasedElementLevelSemanticMatcher;

import java.util.ArrayList;
import java.util.Properties;

/**
 * Implements NGram matcher. See Element Level Semantic matchers paper for more details.
 * 
 * Accepts the following parameters:
 * 

 * threshold - float parameter, which by default equals 0.9.
 * 
 * gramlength - integer parameter which by default equals 3.
 *
 * @author Mikalai Yatskevich [email protected]
 * @author Aliaksandr Autayeu
 */
public class NGram extends Configurable implements IStringBasedElementLevelSemanticMatcher {

    private static final String GRAM_LENGTH_KEY = "gramlength";
    protected int gramlength = 3;

    private static final String THRESHOLD_KEY = "threshold";
    protected double threshold = 0.9;

    @Override
    public boolean setProperties(Properties newProperties) throws ConfigurableException {
        boolean result = super.setProperties(newProperties);
        if (result) {
            if (newProperties.containsKey(GRAM_LENGTH_KEY)) {
                gramlength = Integer.parseInt(newProperties.getProperty(GRAM_LENGTH_KEY));
            }

            if (newProperties.containsKey(THRESHOLD_KEY)) {
                threshold = Double.parseDouble(newProperties.getProperty(THRESHOLD_KEY));
            }
        }
        return result;
    }


    /**
     * Computes the relation with NGram matcher.
     *
     * @param str1 the source input
     * @param str2 the target input
     * @return synonym or IDK relation
     */
    public char match(String str1, String str2) {
        if (null == str1 || null == str2 || 0 == str1.length() || 0 == str2.length()) {
            return IMappingElement.IDK;
        }
        String[] grams1 = generateNGrams(str1, gramlength);
        String[] grams2 = generateNGrams(str2, gramlength);
        int count = 0;
        for (String aGrams1 : grams1)
            for (String aGrams2 : grams2) {
                if (aGrams1.equals(aGrams2)) {
                    count++;
                    break;
                }
            }
        float sim = (float) 2 * count / (grams1.length + grams2.length); // Dice-Coefficient
        if (threshold <= sim) {
            return IMappingElement.EQUIVALENCE;
        } else {
            return IMappingElement.IDK;
        }
    }

    /**
     * Produces nGrams for nGram matcher.
     *
     * @param str        source string
     * @param gramlength gram length
     * @return ngrams
     */
    private static String[] generateNGrams(String str, int gramlength) {
        if (str == null || str.length() == 0) return null;
        ArrayList grams = new ArrayList();
        int length = str.length();
        String gram;
        if (length < gramlength) {
            for (int i = 1; i <= length; i++) {
                gram = str.substring(0, i);
                if (grams.indexOf(gram) == -1) grams.add(gram);
            }
            gram = str.substring(length - 1, length);
            if (grams.indexOf(gram) == -1) grams.add(gram);
        } else {
            for (int i = 1; i <= gramlength - 1; i++) {
                gram = str.substring(0, i);
                if (grams.indexOf(gram) == -1) grams.add(gram);
            }
            for (int i = 0; i < length - gramlength + 1; i++) {
                gram = str.substring(i, i + gramlength);
                if (grams.indexOf(gram) == -1) grams.add(gram);
            }
            for (int i = length - gramlength + 1; i < length; i++) {
                gram = str.substring(i, length);
                if (grams.indexOf(gram) == -1) grams.add(gram);
            }
        }
        return grams.toArray(new String[grams.size()]);
    }
}