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ICU Analysis for Elasticsearch

The ICU Analysis plugin integrates Lucene ICU module into elasticsearch, adding ICU relates analysis components.

In order to install the plugin, simply run:

bin/plugin install elasticsearch/elasticsearch-analysis-icu/2.5.0

You need to install a version matching your Elasticsearch version:

elasticsearch	ICU Analysis Plugin	Docs
master	Build from source	See below
es-1.x	Build from source	2.6.0-SNAPSHOT
es-1.5	2.5.0	2.5.0
es-1.4	2.4.3	2.4.3
< 1.4.5	2.4.2	2.4.2
< 1.4.3	2.4.1	2.4.1
es-1.3	2.3.0	2.3.0
es-1.2	2.2.0	2.2.0
es-1.1	2.1.0	2.1.0
es-1.0	2.0.0	2.0.0
es-0.90	1.13.0	1.13.0

To build a SNAPSHOT version, you need to build it with Maven:

mvn clean install
plugin install analysis-icu \
       --url file:target/releases/elasticsearch-analysis-icu-X.X.X-SNAPSHOT.zip

ICU Normalization

{
    "index" : {
        "analysis" : {
            "analyzer" : {
                "normalized" : {
                    "tokenizer" : "keyword",
                    "filter" : ["icu_normalizer"]
                }
            }
        }
    }
}

ICU Folding

Folding of unicode characters based on UTR#30. It registers itself under icu_folding and icuFolding names. Sample setting:

{
    "index" : {
        "analysis" : {
            "analyzer" : {
                "folded" : {
                    "tokenizer" : "keyword",
                    "filter" : ["icu_folding"]
                }
            }
        }
    }
}

ICU Filtering

The folding can be filtered by a set of unicode characters with the parameter unicodeSetFilter. This is useful for a non-internationalized search engine where retaining a set of national characters which are primary letters in a specific language is wanted. See syntax for the UnicodeSet here.

The Following example exempts Swedish characters from the folding. Note that the filtered characters are NOT lowercased which is why we add that filter below.

{
    "index" : {
        "analysis" : {
            "analyzer" : {
                "folding" : {
                    "tokenizer" : "standard",
                    "filter" : ["my_icu_folding", "lowercase"]
                }
            }
            "filter" : {
                "my_icu_folding" : {
                    "type" : "icu_folding"
                    "unicodeSetFilter" : "[^åäöÅÄÖ]"
                }
            }
        }
    }
}

ICU Collation

Uses collation token filter. Allows to either specify the rules for collation (defined here) using the rules parameter (can point to a location or expressed in the settings, location can be relative to config location), or using the language parameter (further specialized by country and variant). By default registers under icu_collation or icuCollation and uses the default locale.

Here is a sample settings:

{
    "index" : {
        "analysis" : {
            "analyzer" : {
                "collation" : {
                    "tokenizer" : "keyword",
                    "filter" : ["icu_collation"]
                }
            }
        }
    }
}

And here is a sample of custom collation:

{
    "index" : {
        "analysis" : {
            "analyzer" : {
                "collation" : {
                    "tokenizer" : "keyword",
                    "filter" : ["myCollator"]
                }
            },
            "filter" : {
                "myCollator" : {
                    "type" : "icu_collation",
                    "language" : "en"
                }
            }
        }
    }
}

Optional options:

strength - The strength property determines the minimum level of difference considered significant during comparison. The default strength for the Collator is tertiary, unless specified otherwise by the locale used to create the Collator. Possible values: primary, secondary, tertiary, quaternary or identical. See ICU Collation documentation for a more detailed explanation for the specific values.
decomposition - Possible values: no or canonical. Defaults to no. Setting this decomposition property with canonical allows the Collator to handle un-normalized text properly, producing the same results as if the text were normalized. If no is set, it is the user's responsibility to insure that all text is already in the appropriate form before a comparison or before getting a CollationKey. Adjusting decomposition mode allows the user to select between faster and more complete collation behavior. Since a great many of the world's languages do not require text normalization, most locales set no as the default decomposition mode.

Expert options:

alternate - Possible values: shifted or non-ignorable. Sets the alternate handling for strength quaternary to be either shifted or non-ignorable. What boils down to ignoring punctuation and whitespace.
caseLevel - Possible values: true or false. Default is false. Whether case level sorting is required. When strength is set to primary this will ignore accent differences.
caseFirst - Possible values: lower or upper. Useful to control which case is sorted first when case is not ignored for strength tertiary.
numeric - Possible values: true or false. Whether digits are sorted according to numeric representation. For example the value egg-9 is sorted before the value egg-21. Defaults to false.
variableTop - Single character or contraction. Controls what is variable for alternate.
hiraganaQuaternaryMode - Possible values: true or false. Defaults to false. Distinguishing between Katakana and Hiragana characters in quaternary strength .

ICU Tokenizer

Breaks text into words according to UAX #29: Unicode Text Segmentation.

{
    "index" : {
        "analysis" : {
            "analyzer" : {
                "tokenized" : {
                    "tokenizer" : "icu_tokenizer",
                }
            }
        }
    }
}

ICU Normalization CharFilter

Normalizes characters as explained here. It registers itself by default under icu_normalizer or icuNormalizer using the default settings. Allows for the name parameter to be provided which can include the following values: nfc, nfkc, and nfkc_cf. Allows for the mode parameter to be provided which can include the following values: compose and decompose. Use decompose with nfc or nfkc, to get nfd or nfkd, respectively. Here is a sample settings:

{
    "index" : {
        "analysis" : {
            "analyzer" : {
                "normalized" : {
                    "tokenizer" : "keyword",
                    "char_filter" : ["icu_normalizer"]
                }
            }
        }
    }
}

ICU Transform

Transforms are used to process Unicode text in many different ways. Some include case mapping, normalization, transliteration and bidirectional text handling.

You can defined transliterator identifiers by using id property, and specify direction to forward or reverse by using dir property, The default value of both properties are Null and forward.

For example:

{
    "index" : {
        "analysis" : {
            "analyzer" : {
                "latin" : {
                    "tokenizer" : "keyword",
                    "filter" : ["myLatinTransform"]
                }
            },
            "filter" : {
                "myLatinTransform" : {
                    "type" : "icu_transform",
                    "id" : "Any-Latin; NFD; [:Nonspacing Mark:] Remove; NFC"
                }
            }
        }
    }
}

This transform transliterated characters to latin, and separates accents from their base characters, removes the accents, and then puts the remaining text into an unaccented form.

The results are:

你好 to ni hao

здравствуйте to zdravstvujte

こんにちは to kon'nichiha

Currently the filter only supports identifier and direction, custom rulesets are not yet supported.

For more documentation, Please see the user guide of ICU Transform.

License

This software is licensed under the Apache 2 license, quoted below.

Copyright 2009-2014 Elasticsearch <http://www.elasticsearch.org>

Licensed 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.

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