New Stemmers

  Options

New Stemmers

Adding new Stemmers is very simple.

Currently, only English, French, and German stemmers are integrated in to Mobile. But the code is extensible such that you can add new stemmers easily by few steps.

What you need:

  • You'll need two versions of the stemmer; One written in JavaScript, and another in Java. But fortunately, Snowball contains Java stemmers for number of popular languages, and are already included with the package. You can see the full list in Adding support for other (non-CJKV) languages. If your language is listed there, Then you have to find javascript version of the stemmer. Generally, new stemmers are getting added in to Snowball Stemmers in other languages location. If javascript stemmer for your language is available, then download it. Else, you can write a new stemmer in JavaScript using SnowBall algorithm fairly easily. Algorithms are at Snowball.

  • Then, name the JS stemmer exactly like this: {$language-code}_stemmer.js. For example, for Italian(it), name it as, it_stemmer.js. Then, copy it to the docbook-mobile/template_mobile/content/search/stemmers/ folder. (I assumed docbook-mobile is the root folder for mobile.)

    Note

    Make sure you changed the mobile.indexer.language property in build.properties to your language.

  • Now two easy changes needed for the indexer.

    • Open docbook-webhelp/indexer/src/com/nexwave/nquindexer/IndexerTask.java in a text editor and add your language code to the supportedLanguages String Array.

      Example 2. Add new language to supportedLanguages array

      change the Array from, 

      private String[] supportedLanguages= {"en", "de", "fr", "cn", "ja", "ko"}; 
    //currently extended support available for
    // English, German, French and CJK (Chinese, Japanese, Korean) languages only.

      To,

      private String[] supportedLanguages= {"en", "de", "fr", "cn", "ja", "ko", "it"}; 
  //currently extended support available for
  // English, German, French, CJK (Chinese, Japanese, Korean), and Italian languages only.

    • Now, open docbook-webhelp/indexer/src/com/nexwave/nquindexer/SaxHTMLIndex.java and add the following line to the code where it initializes the Stemmer (Search for SnowballStemmer stemmer;). Then add code to initialize the stemmer Object in your language. It's self understandable. See the example. The class names are at: docbook-webhelp/indexer/src/com/nexwave/stemmer/snowball/ext/.

      Example 3. Initialize correct stemmer based on the mobile.indexer.language specified

            SnowballStemmer stemmer;
      if(indexerLanguage.equalsIgnoreCase("en")){
           stemmer = new EnglishStemmer();
      } else if (indexerLanguage.equalsIgnoreCase("de")){
          stemmer= new GermanStemmer();
      } else if (indexerLanguage.equalsIgnoreCase("fr")){
          stemmer= new FrenchStemmer();
      }
else if (indexerLanguage.equalsIgnoreCase("it")){ //If language code is "it" (Italian)
          stemmer= new italianStemmer();  //Initialize the stemmer to italianStemmer object.
      }       
      else {
          stemmer = null;
      }

That's all. Now run ant build-indexer to compile and build the java code. Then, run ant mobile to generate the output from your docbook file. For any questions, contact us or email to the docbook mailing list .