This is an implementation of a word decompounder plugin for Elasticsearch.
This word decompounding token filter is complementing the standard Elasticsearch compound word token filter.
Compounding several words into one word is a property not all languages share. Compounding is used in German, Scandinavian Languages, Finnish and Korean.
This code is a reworked implementation of
the Baseforms Tool
found in the ASV toolbox
of Chris Biemann,
Automatische Sprachverarbeitung of Leipzig University.
Lucene comes with two coumpound word token filters, a dictionary- and a hyphenation-based variant. Both of them have a disadvantage, they require loading a word list in memory before they run. This decompounder does not require word lists, it can process german language text out of the box. The decompounder uses prebuilt Compact Patricia Tries for efficient word segmentation provided by the ASV toolbox.
| Plugin version | Elasticsearch version | Release date |
|---|---|---|
| 2.3.4.0 | 2.3.4 | Jul 30 2016 |
| 2.3.3.0 | 2.3.3 | Jun 1 2016 |
| 2.3.2.0 | 2.3.2 | Jun 1 2016 |
| 2.3.1.0 | 2.3.1 | Jun 1 2016 |
| 2.3.0.0 | 2.3.0 | Mar 31 2016 |
| 2.2.1.0 | 2.2.1 | Mar 31 2016 |
| 2.2.0.0 | 2.2.0 | Feb 19 2016 |
| 2.1.1.0 | 2.1.1 | Dec 22 2015 |
| 2.1.0.0 | 2.1.0 | Dec 8 2015 |
| 1.7.1.3 | 1.7.1 | Nov 17 2015 |
| 1.5.2.0 | 1.5.2 | Oct 26 2015 |
./bin/plugin install http://xbib.org/repository/org/xbib/elasticsearch/plugin/elasticsearch-analysis-decompound/2.3.4.0/elasticsearch-analysis-decompound-2.3.4.0-plugin.zip
./bin/plugin -install decompound -url http://xbib.org/repository/org/xbib/elasticsearch/plugin/elasticsearch-analysis-decompound/1.7.1.3/elasticsearch-analysis-decompound-1.7.1.3-plugin.zip
Do not forget to restart the node after installing.
The Maven project site is available at Github
All feedback is welcome! If you find issues, please post them at Github
In the mapping, us a token filter of type "decompound"::
{ "index":{ "analysis":{ "filter":{ "decomp":{ "type" : "decompound" } }, "tokenizer" : { "decomp" : { "type" : "standard", "filter" : [ "decomp" ] } } } } }
"Die Jahresfeier der Rechtsanwaltskanzleien auf dem Donaudampfschiff hat viel Ökosteuer gekostet" will be tokenized into "Die", "Die", "Jahresfeier", "Jahr", "feier", "der", "der", "Rechtsanwaltskanzleien", "Recht", "anwalt", "kanzlei", "auf", "auf", "dem", "dem", "Donaudampfschiff", "Donau", "dampf", "schiff", "hat", "hat", "viel", "viel", "Ökosteuer", "Ökosteuer", "gekostet", "gekosten"
It is recommended to add the Unique token filter <http://www.elasticsearch.org/guide/reference/index-modules/analysis/unique-tokenfilter.html>_ to skip tokens that occur more than once.
Also the Lucene german normalization token filter is provided::
{
"index":{
"analysis":{
"filter":{
"umlaut":{
"type":"german_normalize"
}
},
"tokenizer" : {
"umlaut" : {
"type":"standard",
"filter" : "umlaut"
}
}
}
}
}
The input "Ein schöner Tag in Köln im Café an der Straßenecke" will be tokenized into "Ein", "schoner", "Tag", "in", "Koln", "im", "Café", "an", "der", "Strassenecke".
The decomposing algorithm knows about a threshold when to assume words as decomposed successfully or not. If the threshold is too low, words could silently disappear from being indexed. In this case, you have to adapt the threshold so words do no longer disappear.
The default threshold value is 0.51. You can modify it in the settings::
{
"index" : {
"analysis" : {
"filter" : {
"decomp" : {
"type" : "decompound",
"threshold" : 0.51
}
},
"tokenizer" : {
"decomp" : {
"type" : "standard",
"filter" : [ "decomp" ]
}
}
}
}
}
Sometimes only the decomposed subwords should be indexed. For this, you can use the parameter "subwords_only": true
{
"index" : {
"analysis" : {
"filter" : {
"decomp" : {
"type" : "decompound",
"subwords_only" : true
}
},
"tokenizer" : {
"decomp" : {
"type" : "standard",
"filter" : [ "decomp" ]
}
}
}
}
}
The Compact Patricia Trie data structure can be found in
Morrison, D.: Patricia - practical algorithm to retrieve information coded in alphanumeric. Journal of ACM, 1968, 15(4):514–534
The compound splitter used for generating features for document classification is described in
Witschel, F., Biemann, C.: Rigorous dimensionality reduction through linguistically motivated feature selection for text categorization. Proceedings of NODALIDA 2005, Joensuu, Finland
The base form reduction step (for Norwegian) is described in
Eiken, U.C., Liseth, A.T., Richter, M., Witschel, F. and Biemann, C.: Ord i Dag: Mining Norwegian Daily Newswire. Proceedings of FinTAL, Turku, 2006, Finland
Decompounder Analysis Plugin for Elasticsearch
Copyright (C) 2012 Jörg Prante
Derived work of ASV toolbox http://asv.informatik.uni-leipzig.de/asv/methoden
Copyright (C) 2005 Abteilung Automatische Sprachverarbeitung, Institut für Informatik, Universität Leipzig
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.
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.
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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.