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https://issues.apache.org/jira/browse/LUCENE-4286?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13429480#comment-13429480
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Lance Norskog commented on LUCENE-4286:
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If you do unigrams and bigrams in separate fields, you can bias bigrams over
unigrams. We did that with one customer and it really helped. Our text was
technical and tended towards "long" words: lots of bigrams & trigrams. Have you
tried the Smart Chinese toolkit? It produces a lot less bigrams. Our project
worked well with it. I would try that, with misfires further broken into
bigrams, over general bigramming. C.f. [SOLR-3653] about the "misfires" part.
In general we found Chinese-language search a really hard problem, and doubly
so when nobody on the team speaks Chinese.
> Add flag to CJKBigramFilter to allow indexing unigrams as well as bigrams
> -------------------------------------------------------------------------
>
> Key: LUCENE-4286
> URL: https://issues.apache.org/jira/browse/LUCENE-4286
> Project: Lucene - Core
> Issue Type: Improvement
> Affects Versions: 4.0-ALPHA, 3.6.1
> Reporter: Tom Burton-West
> Priority: Minor
> Fix For: 4.0, 5.0
>
> Attachments: LUCENE-4286.patch, LUCENE-4286.patch
>
>
> 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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