Consider different query and index segmentation for Japanese
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Key: LUCENE-3916
URL: https://issues.apache.org/jira/browse/LUCENE-3916
Project: Lucene - Java
Issue Type: Improvement
Components: modules/analysis
Affects Versions: 3.6, 4.0
Reporter: Christian Moen
Priority: Minor
Kuromoji today uses search mode segmentation both at query and index time.
The benefit with search mode segmentation is that it segments compounds such as
関西国際空港 (Kansai International Airport) into 関西 (Kansai), 国際 (international), 空港
(airport), and leaves the compound 関西国際空港 as a synonym to 関西.
This segmentation allows us to get a match for 空港 (airport), which is good for
recall and we'd get good precision when searching for the compound 関西国際空港
because of IDF.
However, if we search for the compound 関西国際空港 (Kansai International Airport)
our query becomes (by default) an OR-query with terms 関西 (Kansai), 関西国際空港
(Kansai International Airport), 国際 (international) and 空港 (airport).
This behaviour is by-design when using OR as the default operator, but this
also has the effect of returning generic hits like 空港 (airport) when the user
searches for something very specific like 関西国際空港 (Kansai International Airport)
-- and these hits are also highlighted.
This doesn't necessarily mean that ranking is flawed per se, but a user or
application might prefer precision over recall. In order to favour precision,
we can consider using normal mode segmentation for queries, but retain search
mode segmentation on the indexing side.
Does anyone have any general opinion on this? What would we do for other
language in the case of compound splitting?
Perhaps this can be dealt with as a documentation issue with a comment in
{{schema.xml}} while keeping the current behaviour?
Many thanks for any input.
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