Elasticsearch: The Definitive Guide

Chapter 18. Getting Started with Languages

Elasticsearch ships with a collection of language analyzers that provide good, basic, out-of-the-box support for many of the world’s most common languages:

Arabic, Armenian, Basque, Brazilian, Bulgarian, Catalan, Chinese, Czech, Danish, Dutch, English, Finnish, French, Galician, German, Greek, Hindi, Hungarian, Indonesian, Irish, Italian, Japanese, Korean, Kurdish, Norwegian, Persian, Portuguese, Romanian, Russian, Spanish, Swedish, Turkish, and Thai.

These analyzers typically perform four roles:

• Tokenize text into individual words:

  The quick brown foxes → [The, quick, brown, foxes]

• Lowercase tokens:

  The → the

• Remove common stopwords:

  [The, quick, brown, foxes] → [quick, brown, foxes]

• Stem tokens to their root form:

  foxes → fox

Each analyzer may also apply other transformations specific to its language in order to make words from that language more searchable:

• The english analyzer removes the possessive 's:

  John's → john

• The french analyzer removes elisions like l' and qu' and diacritics like ¨ or ^:

  l'église → eglis

• The german analyzer normalizes terms, replacing ä and ae with a, or ß with ss, among others:

  äußerst → ausserst

Using Language Analyzers

The built-in language analyzers are available globally and don’t need to be configured before being used. They can be specified directly in the field mapping:

PUT /my_index
{
  "mappings": {
    "blog": {
      "properties": {
        "title": {
          "type":     "string",
          "analyzer": "english"