source: trunk/gli/src/org/greenstone/gatherer/util/MED.java@ 4364

/**
 *#########################################################################
 *
 * A component of the Gatherer application, part of the Greenstone digital
 * library suite from the New Zealand Digital Library Project at the
 * University of Waikato, New Zealand.
 *
 * <BR><BR>
 *
 * Author: John Thompson, Greenstone Digital Library, University of Waikato
 *
 * <BR><BR>
 *
 * Copyright (C) 1999 New Zealand Digital Library Project
 *
 * <BR><BR>
 *
 * This program 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 2 of the License, or
 * (at your option) any later version.
 *
 * <BR><BR>
 *
 * This program 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.
 *
 * <BR><BR>
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *########################################################################
 */

 




/* GPL_HEADER */
package org.greenstone.gatherer.util;
/**************************************************************************************
 * Title:        Gatherer
 * Description:  The Gatherer: a tool for gathering and enriching a digital collection.
 * Company:      The University of Waikato
 * Written:      28/08/02
 * Revised:      
 * @author John Thompson, 9826509
 * @author Michael Gilleland, Merriam Park Software
 * @version 2.3
 **************************************************************************************/
/** Determines the MED between two metadata element names.<BR>
 * Adapted from code by Michael Gilleland, Merriam Park Software, as detailed in a short essay called "Levenshtein Distance, in Three Flavors" available at http://www.merriampark.com/ld.htm.
 */
public class MED {
    //****************************
    // Get minimum of three values
    //****************************
    static private int Minimum (int a, int b, int c) {
    int mi = a;
    if (b < mi) {
        mi = b;
    }
    if (c < mi) {
        mi = c;
    }
    return mi;
    }
    //*****************************
    // Compute Levenshtein distance
    //*****************************
    static public int LD (String s, String t) {
    int d[][]; // matrix
    int n; // length of s
    int m; // length of t
    int i; // iterates through s
    int j; // iterates through t
    char s_i; // ith character of s
    char t_j; // jth character of t
    int cost; // cost
    // Step 1
    // Set n to be the length of s.
    // Set m to be the length of t.
    // If n = 0, return m and exit.
    // If m = 0, return n and exit.
    // Construct a matrix containing 0..m rows and 0..n columns.
    n = s.length ();
    m = t.length ();
    if (n == 0) {
        return m;
    }
    if (m == 0) {
        return n;
    }
    d = new int[n+1][m+1];
    // Step 2
    // Initialize the first row to 0..n.
    // Initialize the first column to 0..m.
    for (i = 0; i <= n; i++) {
        d[i][0] = i;
    }
    for (j = 0; j <= m; j++) {
        d[0][j] = j;
    }
    // Step 3
    // Examine each character of s (i from 1 to n).
    for (i = 1; i <= n; i++) {
        s_i = s.charAt (i - 1);
                // Step 4
                // Examine each character of t (j from 1 to m).
        for (j = 1; j <= m; j++) {
        t_j = t.charAt (j - 1);
        // Step 5
        // If s[i] equals t[j], the cost is 0.
        // If s[i] doesn't equal t[j], the cost is 1.
        if (s_i == t_j) {
            cost = 0;
        }
        else {
            cost = 1;
        }
        // Step 6
        // Set cell d[i,j] of the matrix equal to the minimum of:
        // a. The cell immediately above plus 1: d[i-1,j] + 1.
        // b. The cell immediately to the left plus 1: d[i,j-1] + 1.
        // c. The cell diagonally above and to the left plus the cost: d[i-1,j-1] + cost.
        d[i][j] = Minimum (d[i-1][j]+1, d[i][j-1]+1, d[i-1][j-1] + cost);
        }
    }
    // Step 7
    // After the iteration steps (3, 4, 5, 6) are complete, the distance is found in cell d[n,m].
    int result = d[n][m];
    d = null;
    return result;
    }
}