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From "Tom Burton-West (JIRA)" <>
Subject [jira] [Created] (LUCENE-4286) Add flag to CJKBigramFilter to allow indexing unigrams as well is bigrams
Date Fri, 03 Aug 2012 22:58:02 GMT
Tom Burton-West created LUCENE-4286:

             Summary: Add flag to CJKBigramFilter to allow indexing unigrams as well is bigrams
                 Key: LUCENE-4286
             Project: Lucene - Core
          Issue Type: Improvement
    Affects Versions: 3.6.1, 4.0-ALPHA
            Reporter: Tom Burton-West
            Priority: Minor

Add an optional  flag to the CJKBigramFilter to tell it to also output unigrams.   This would
allow indexing of both bigrams and unigrams and at query time the analyzer could analyze queries
as bigrams unless the query contained a single Han unigram.

As an example here is a configuration a Solr fieldType with the analyzer for indexing with
the "indexUnigrams" flag set and the analyzer for querying without the flag. 

<fieldType name="CJK" autoGeneratePhraseQueries="false">
<analyzer type="index">
   <tokenizer class="solr.ICUTokenizerFactory"/>
   <filter class="solr.CJKBigramFilterFactory" indexUnigrams="true" han="true"/>

<analyzer type="query">
   <tokenizer class="solr.ICUTokenizerFactory"/>
   <filter class="solr.CJKBigramFilterFactory" han="true"/>

Use case: About 10% of our queries that contain Han characters are single character queries.
  The CJKBigram filter only outputs single characters when there are no adjacent bigrammable
characters in the input.  This means we have to create a separate field to index Han unigrams
in order to address single character queries and then write application code to search that
separate field if we detect a single character Han query.  This is rather kludgey.  With the
optional flag, we could configure Solr as above  

This is somewhat analogous to the flags in LUCENE-1370 for the ShingleFilter used to allow
single word queries (although that uses word n-grams rather than character n-grams.)

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