[[analysis-compound-word-tokenfilter]]
=== Compound Word Token Filter

The `hyphenation_decompounder` and `dictionary_decompounder` token filters can
decompose compound words found in many German languages into word parts.

Both token filters require a dictionary of word parts, which can be provided
as:

[horizontal]
`word_list`::

An array of words, specified inline in the token filter configuration, or

`word_list_path`::

The path (either absolute or relative to the `config` directory) to a UTF-8
encoded file containing one word per line.

[float]
=== Hyphenation decompounder

The `hyphenation_decompounder` uses hyphenation grammars to find potential
subwords that are then checked against the word dictionary. 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.

XML based hyphenation grammar files can be found in the
http://offo.sourceforge.net/hyphenation/#FOP+XML+Hyphenation+Patterns[Objects For Formatting Objects]
(OFFO) Sourceforge project. You can download http://downloads.sourceforge.net/offo/offo-hyphenation.zip[offo-hyphenation.zip]
directly and look in the `offo-hyphenation/hyph/` directory.
Credits for the hyphenation code go to the Apache FOP project .

[float]
=== Dictionary decompounder

The `dictionary_decompounder` uses a brute force approach in conjuction with
only the word dictionary to find subwords in a compound word. It is much
slower than the hyphenation decompounder but can be used as a first start to
check the quality of your dictionary.

[float]
=== Compound token filter parameters

The following parameters can be used to configure a compound word token
filter:

[horizontal]
`type`::

Either `dictionary_decompounder` or `hyphenation_decompounder`.

`word_list`::

A array containing a list of words to use for the word dictionary.

`word_list_path`::

The path (either absolute or relative to the `config` directory) to the word dictionary.

`hyphenation_patterns_path`::

The path (either absolute or relative to the `config` directory) to a FOP XML hyphenation pattern file. (required for hyphenation)

`min_word_size`::

Minimum word size. Defaults to 5.

`min_subword_size`::

Minimum subword size. Defaults to 2.

`max_subword_size`::

Maximum subword size. Defaults to 15.

`only_longest_match`::

Whether to include only the longest matching subword or not.  Defaults to `false`


Here is an example:

[source,js]
--------------------------------------------------
index :
    analysis :
        analyzer :
            myAnalyzer2 :
                type : custom
                tokenizer : standard
                filter : [myTokenFilter1, myTokenFilter2]
        filter :
            myTokenFilter1 :
                type : dictionary_decompounder
                word_list: [one, two, three]
            myTokenFilter2 :
                type : hyphenation_decompounder
                word_list_path: path/to/words.txt
                hyphenation_patterns_path: path/to/fop.xml
                max_subword_size : 22
--------------------------------------------------
