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https://issues.apache.org/jira/browse/SOLR-4381?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13621944#comment-13621944
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Okke Klein commented on SOLR-4381:
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The terms that are being expanded by the solr.SynonymFilterFactory are also
being stemmed. This is unwanted if you want to expand "MIA" to "missing in
action" and not "miss in action". See [Github
issue|https://github.com/healthonnet/hon-lucene-synonyms/issues/14] for details.
> Query-time multi-word synonym expansion
> ---------------------------------------
>
> Key: SOLR-4381
> URL: https://issues.apache.org/jira/browse/SOLR-4381
> Project: Solr
> Issue Type: Improvement
> Components: query parsers
> Reporter: Nolan Lawson
> Priority: Minor
> Labels: multi-word, queryparser, synonyms
> Fix For: 4.3
>
> Attachments: SOLR-4381-2.patch, SOLR-4381.patch
>
>
> This is an issue that seems to come up perennially.
> The [Solr
> docs|http://wiki.apache.org/solr/AnalyzersTokenizersTokenFilters#solr.SynonymFilterFactory]
> caution that index-time synonym expansion should be preferred to query-time
> synonym expansion, due to the way multi-word synonyms are treated and how IDF
> values can be boosted artificially. But query-time expansion should have huge
> benefits, given that changes to the synonyms don't require re-indexing, the
> index size stays the same, and the IDF values for the documents don't get
> permanently altered.
> The proposed solution is to move the synonym expansion logic from the
> analysis chain (either query- or index-type) and into a new QueryParser. See
> the attached patch for an implementation.
> The core Lucene functionality is untouched. Instead, the EDismaxQParser is
> extended, and synonym expansion is done on-the-fly. Queries are parsed into
> a lattice (i.e. all possible synonym combinations), while individual
> components of the query are still handled by the EDismaxQParser itself.
> It's not an ideal solution by any stretch. But it's nice and self-contained,
> so it invites experimentation and improvement. And I think it fits in well
> with the merry band of misfit query parsers, like {{func}} and {{frange}}.
> More details about this solution can be found in [this blog
> post|http://nolanlawson.com/2012/10/31/better-synonym-handling-in-solr/] and
> [the Github page for the
> code|https://github.com/healthonnet/hon-lucene-synonyms].
> At the risk of tooting my own horn, I also think this patch sufficiently
> fixes SOLR-3390 (highlighting problems with multi-word synonyms) and
> LUCENE-4499 (better support for multi-word synonyms).
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