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+<html>
+<head>
+<title>CompoundWordTokenFilter</title>
+<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"></meta>
+</head>
+<body>
+A filter that decomposes compound words you find in many Germanic
+languages into the word parts. This example shows what it does:
+<table border="1">
+ <tr>
+ <th>Input token stream</th>
+ </tr>
+ <tr>
+ <td>Rindfleischüberwachungsgesetz Drahtschere abba</td>
+ </tr>
+</table>
+<br>
+<table border="1">
+ <tr>
+ <th>Output token stream</th>
+ </tr>
+ <tr>
+ <td>(Rindfleischüberwachungsgesetz,0,29)</td>
+ </tr>
+ <tr>
+ <td>(Rind,0,4,posIncr=0)</td>
+ </tr>
+ <tr>
+ <td>(fleisch,4,11,posIncr=0)</td>
+ </tr>
+ <tr>
+ <td>(überwachung,11,22,posIncr=0)</td>
+ </tr>
+ <tr>
+ <td>(gesetz,23,29,posIncr=0)</td>
+ </tr>
+ <tr>
+ <td>(Drahtschere,30,41)</td>
+ </tr>
+ <tr>
+ <td>(Draht,30,35,posIncr=0)</td>
+ </tr>
+ <tr>
+ <td>(schere,35,41,posIncr=0)</td>
+ </tr>
+ <tr>
+ <td>(abba,42,46)</td>
+ </tr>
+</table>
+
+The input token is always preserved and the filters do not alter the case of word parts. There are two variants of the
+filter available:
+<ul>
+ <li><i>HyphenationCompoundWordTokenFilter</i>: it uses a
+ hyphenation grammar based approach to find potential word parts of a
+ given word.</li>
+ <li><i>DictionaryCompoundWordTokenFilter</i>: it uses a
+ brute-force dictionary-only based approach to find the word parts of a given
+ word.</li>
+</ul>
+
+<h3>Compound word token filters</h3>
+<h4>HyphenationCompoundWordTokenFilter</h4>
+The {@link
+org.apache.lucene.analysis.compound.HyphenationCompoundWordTokenFilter
+HyphenationCompoundWordTokenFilter} uses hyphenation grammars to find
+potential subwords that a worth to check against the dictionary. It can be used
+without a dictionary as well but then produces a lot of "nonword" tokens.
+The quality of the output tokens is directly connected to the quality of the
+grammar file you use. For languages like German they are quite good.
+<h5>Grammar file</h5>
+Unfortunately we cannot bundle the hyphenation grammar files with Lucene
+because they do not use an ASF compatible license (they use the LaTeX
+Project Public License instead). You can find the XML based grammar
+files at the
+<a href="http://offo.sourceforge.net/hyphenation/index.html">Objects
+For Formatting Objects</a>
+(OFFO) Sourceforge project (direct link to download the pattern files:
+<a href="http://downloads.sourceforge.net/offo/offo-hyphenation.zip">http://downloads.sourceforge.net/offo/offo-hyphenation.zip</a>
+). The files you need are in the subfolder
+<i>offo-hyphenation/hyph/</i>
+.
+<br />
+Credits for the hyphenation code go to the
+<a href="http://xmlgraphics.apache.org/fop/">Apache FOP project</a>
+.
+
+<h4>DictionaryCompoundWordTokenFilter</h4>
+The {@link
+org.apache.lucene.analysis.compound.DictionaryCompoundWordTokenFilter
+DictionaryCompoundWordTokenFilter} uses a dictionary-only approach to
+find subwords in a compound word. It is much slower than the one that
+uses the hyphenation grammars. You can use it as a first start to
+see if your dictionary is good or not because it is much simpler in design.
+
+<h3>Dictionary</h3>
+The output quality of both token filters is directly connected to the
+quality of the dictionary you use. They are language dependent of course.
+You always should use a dictionary
+that fits to the text you want to index. If you index medical text for
+example then you should use a dictionary that contains medical words.
+A good start for general text are the dictionaries you find at the
+<a href="http://wiki.services.openoffice.org/wiki/Dictionaries">OpenOffice
+dictionaries</a>
+Wiki.
+
+<h3>Which variant should I use?</h3>
+This decision matrix should help you:
+<table border="1">
+ <tr>
+ <th>Token filter</th>
+ <th>Output quality</th>
+ <th>Performance</th>
+ </tr>
+ <tr>
+ <td>HyphenationCompoundWordTokenFilter</td>
+ <td>good if grammar file is good – acceptable otherwise</td>
+ <td>fast</td>
+ </tr>
+ <tr>
+ <td>DictionaryCompoundWordTokenFilter</td>
+ <td>good</td>
+ <td>slow</td>
+ </tr>
+</table>
+<h3>Examples</h3>
+<pre>
+ public void testHyphenationCompoundWordsDE() throws Exception {
+ String[] dict = { "Rind", "Fleisch", "Draht", "Schere", "Gesetz",
+ "Aufgabe", "Überwachung" };
+
+ Reader reader = new FileReader("de_DR.xml");
+
+ HyphenationTree hyphenator = HyphenationCompoundWordTokenFilter
+ .getHyphenationTree(reader);
+
+ HyphenationCompoundWordTokenFilter tf = new HyphenationCompoundWordTokenFilter(
+ new WhitespaceTokenizer(new StringReader(
+ "Rindfleischüberwachungsgesetz Drahtschere abba")), hyphenator,
+ dict, CompoundWordTokenFilterBase.DEFAULT_MIN_WORD_SIZE,
+ CompoundWordTokenFilterBase.DEFAULT_MIN_SUBWORD_SIZE,
+ CompoundWordTokenFilterBase.DEFAULT_MAX_SUBWORD_SIZE, false);
+
+ CharTermAttribute t = tf.addAttribute(CharTermAttribute.class);
+ while (tf.incrementToken()) {
+ System.out.println(t);
+ }
+ }
+
+ public void testHyphenationCompoundWordsWithoutDictionaryDE() throws Exception {
+ Reader reader = new FileReader("de_DR.xml");
+
+ HyphenationTree hyphenator = HyphenationCompoundWordTokenFilter
+ .getHyphenationTree(reader);
+
+ HyphenationCompoundWordTokenFilter tf = new HyphenationCompoundWordTokenFilter(
+ new WhitespaceTokenizer(new StringReader(
+ "Rindfleischüberwachungsgesetz Drahtschere abba")), hyphenator);
+
+ CharTermAttribute t = tf.addAttribute(CharTermAttribute.class);
+ while (tf.incrementToken()) {
+ System.out.println(t);
+ }
+ }
+
+ public void testDumbCompoundWordsSE() throws Exception {
+ String[] dict = { "Bil", "Dörr", "Motor", "Tak", "Borr", "Slag", "Hammar",
+ "Pelar", "Glas", "Ögon", "Fodral", "Bas", "Fiol", "Makare", "Gesäll",
+ "Sko", "Vind", "Rute", "Torkare", "Blad" };
+
+ DictionaryCompoundWordTokenFilter tf = new DictionaryCompoundWordTokenFilter(
+ new WhitespaceTokenizer(
+ new StringReader(
+ "Bildörr Bilmotor Biltak Slagborr Hammarborr Pelarborr Glasögonfodral Basfiolsfodral Basfiolsfodralmakaregesäll Skomakare Vindrutetorkare Vindrutetorkarblad abba")),
+ dict);
+ CharTermAttribute t = tf.addAttribute(CharTermAttribute.class);
+ while (tf.incrementToken()) {
+ System.out.println(t);
+ }
+ }
+</pre>
+</body>
+</html>
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fnp / pylucene.git / blobdiff