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https://issues.apache.org/jira/browse/LUCENE-1622?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12703790#action_12703790
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Earwin Burrfoot commented on LUCENE-1622:
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I'll shortly cite my experiences mentioned on the list.
* Injecting "synonym group id" token instead of all tokens for all synonyms in
group is a big win with index size and saves you from matching for "big". It
also plays better with highlighting (still had to rewrite it to handle all
corner cases).
* Properly handling multiword synonyms only on index-side is impossible, you
have to dabble in query rewriting (even then low-probability corner cases
exist, and you might find extra docs).
* Query expansion is the only absolutely clear way to have multiword synonyms
with current Lucene, but it is impractical on any adequate synonym dictionary.
* There is a possible change to the way Lucene indexes tokens+positions to
enable fully proper multiword synonyms - adding a notion of 'length' or 'span'
to a token, this length should play together with positionIncrement when
calculating distance between tokens in phrase/spannear queries.
> Multi-word synonym filter (synonym expansion at indexing time).
> ---------------------------------------------------------------
>
> Key: LUCENE-1622
> URL: https://issues.apache.org/jira/browse/LUCENE-1622
> Project: Lucene - Java
> Issue Type: New Feature
> Components: contrib/*
> Reporter: Dawid Weiss
> Priority: Minor
> Attachments: synonyms.patch
>
>
> It would be useful to have a filter that provides support for indexing-time
> synonym expansion, especially for multi-word synonyms (with multi-word
> matching for original tokens).
> The problem is not trivial, as observed on the mailing list. The problems I
> was able to identify (mentioned in the unit tests as well):
> - if multi-word synonyms are indexed together with the original token stream
> (at overlapping positions), then a query for a partial synonym sequence
> (e.g., "big" in the synonym "big apple" for "new york city") causes the
> document to match;
> - there are problems with highlighting the original document when synonym is
> matched (see unit tests for an example),
> - if the synonym is of different length than the original sequence of tokens
> to be matched, then phrase queries spanning the synonym and the original
> sequence boundary won't be found. Example "big apple" synonym for "new york
> city". A phrase query "big apple restaurants" won't match "new york city
> restaurants".
> I am posting the patch that implements phrase synonyms as a token filter.
> This is not necessarily intended for immediate inclusion, but may provide a
> basis for many people to experiment and adjust to their own scenarios.
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