Tom Burton-West created LUCENE-4286:
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Summary: Add flag to CJKBigramFilter to allow indexing unigrams as
well is bigrams
Key: LUCENE-4286
URL: https://issues.apache.org/jira/browse/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>
<analyzer type="query">
<tokenizer class="solr.ICUTokenizerFactory"/>
<filter class="solr.CJKBigramFilterFactory" han="true"/>
</analyzer>
</fieldType>
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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