package org.apache.lucene.analysis.ar; /** * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You 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. */ /** * Stemmer for Arabic. * <p> * Stemming is done in-place for efficiency, operating on a termbuffer. * <p> * Stemming is defined as: * <ul> * <li> Removal of attached definite article, conjunction, and prepositions. * <li> Stemming of common suffixes. * </ul> * */ public class ArabicStemmer { public static final char ALEF = '\u0627'; public static final char BEH = '\u0628'; public static final char TEH_MARBUTA = '\u0629'; public static final char TEH = '\u062A'; public static final char FEH = '\u0641'; public static final char KAF = '\u0643'; public static final char LAM = '\u0644'; public static final char NOON = '\u0646'; public static final char HEH = '\u0647'; public static final char WAW = '\u0648'; public static final char YEH = '\u064A'; public static final char prefixes[][] = { ("" + ALEF + LAM).toCharArray(), ("" + WAW + ALEF + LAM).toCharArray(), ("" + BEH + ALEF + LAM).toCharArray(), ("" + KAF + ALEF + LAM).toCharArray(), ("" + FEH + ALEF + LAM).toCharArray(), ("" + LAM + LAM).toCharArray(), ("" + WAW).toCharArray(), }; public static final char suffixes[][] = { ("" + HEH + ALEF).toCharArray(), ("" + ALEF + NOON).toCharArray(), ("" + ALEF + TEH).toCharArray(), ("" + WAW + NOON).toCharArray(), ("" + YEH + NOON).toCharArray(), ("" + YEH + HEH).toCharArray(), ("" + YEH + TEH_MARBUTA).toCharArray(), ("" + HEH).toCharArray(), ("" + TEH_MARBUTA).toCharArray(), ("" + YEH).toCharArray(), }; /** * Stem an input buffer of Arabic text. * * @param s input buffer * @param len length of input buffer * @return length of input buffer after normalization */ public int stem(char s[], int len) { len = stemPrefix(s, len); len = stemSuffix(s, len); return len; } /** * Stem a prefix off an Arabic word. * @param s input buffer * @param len length of input buffer * @return new length of input buffer after stemming. */ public int stemPrefix(char s[], int len) { for (int i = 0; i < prefixes.length; i++) if (startsWith(s, len, prefixes[i])) return deleteN(s, 0, len, prefixes[i].length); return len; } /** * Stem suffix(es) off an Arabic word. * @param s input buffer * @param len length of input buffer * @return new length of input buffer after stemming */ public int stemSuffix(char s[], int len) { for (int i = 0; i < suffixes.length; i++) if (endsWith(s, len, suffixes[i])) len = deleteN(s, len - suffixes[i].length, len, suffixes[i].length); return len; } /** * Returns true if the prefix matches and can be stemmed * @param s input buffer * @param len length of input buffer * @param prefix prefix to check * @return true if the prefix matches and can be stemmed */ boolean startsWith(char s[], int len, char prefix[]) { if (prefix.length == 1 && len < 4) { // wa- prefix requires at least 3 characters return false; } else if (len < prefix.length + 2) { // other prefixes require only 2. return false; } else { for (int i = 0; i < prefix.length; i++) if (s[i] != prefix[i]) return false; return true; } } /** * Returns true if the suffix matches and can be stemmed * @param s input buffer * @param len length of input buffer * @param suffix suffix to check * @return true if the suffix matches and can be stemmed */ boolean endsWith(char s[], int len, char suffix[]) { if (len < suffix.length + 2) { // all suffixes require at least 2 characters after stemming return false; } else { for (int i = 0; i < suffix.length; i++) if (s[len - suffix.length + i] != suffix[i]) return false; return true; } } /** * Delete n characters in-place * * @param s Input Buffer * @param pos Position of character to delete * @param len Length of input buffer * @param nChars number of characters to delete * @return length of input buffer after deletion */ protected int deleteN(char s[], int pos, int len, int nChars) { for (int i = 0; i < nChars; i++) len = delete(s, pos, len); return len; } /** * Delete a character in-place * * @param s Input Buffer * @param pos Position of character to delete * @param len length of input buffer * @return length of input buffer after deletion */ protected int delete(char s[], int pos, int len) { if (pos < len) System.arraycopy(s, pos + 1, s, pos, len - pos - 1); return len - 1; } }