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From "James Dyer (JIRA)" <>
Subject [jira] [Commented] (SOLR-2585) Context-Sensitive Spelling Suggestions & Collations
Date Mon, 19 Sep 2011 15:00:11 GMT


James Dyer commented on SOLR-2585:


I was thinking of maybe eventually submitting some refactorings as a follow-up to this issue.
 But if you want, we could do some things first then come back to this.  Here were my initial
thoughts, none of which are very well-though-out at this point...

1. Maybe move "FileBasedSpellChecker" to Lucene for consistency (each spell checker in Solr
refers to a Spell checker in Lucene).  Also, this makes it available to Lucene users.

2. Perhaps SpellingOptions could somehow be deleted.

3. If the Lucene Spell Checkers all inherited a common interface and/or Abstract Class, all
of the *SolrSpellChecker classes could probably be reduced to 1 class (or 1 parent class with
just a few overrides here and there...) (I know you feel we're not ready for this, but we
could annotate the Lucene parent (class and/or interface) like this for now "@lucene.internal
- external users should use the appropriate subclass directly / @lucene.experimental - this
[class|interface] may change or be removed in a future version").  

4. Clarify the code in SpellCheckComponent.  Wasn't thinking about this now, but I do see
where you're coming from, especially with the distributed code in "finishStage".  I think
there is some code duplication between "finishStage" (distributed) and "process" (non-dist
/ 1st stage dist) that can maybe be eliminated.  Probably some good code comments would help
de-mystify this too.  Maybe rename a method or two for additional clarity.

5. Now that you point out that "instanceof" check in "finishStage", we probably should write
a test case with DirectSpellChecker in a distributed environment.  Possibly a revamped (set
of) *SolrSpellChecker class(es) could eliminate the need for such checks?

6. I think SpellingParams should be for parameters the user can put in their query.  I'm not
sure you can do this with "accuracy".  This one should probably be somewhere else as this
is a SearchComponent config param, not a request param.  Maybe there are others like this.

> Context-Sensitive Spelling Suggestions & Collations
> ---------------------------------------------------
>                 Key: SOLR-2585
>                 URL:
>             Project: Solr
>          Issue Type: Improvement
>          Components: spellchecker
>    Affects Versions: 4.0
>            Reporter: James Dyer
>            Priority: Minor
>         Attachments: SOLR-2585.patch, SOLR-2585.patch, SOLR-2585.patch, SOLR-2585.patch,
> Solr currently cannot offer what I'm calling here a "context-sensitive" spelling suggestion.
 That is, if a user enters one or more words that have docFrequency > 0, but nevertheless
are misspelled, then no suggestions are offered.  Currently, Solr will always consider a word
"correctly spelled" if it is in the index and/or dictionary, regardless of context.  This
issue & patch add support for context-sensitive spelling suggestions. 
> See SpellCheckCollatorTest.testContextSensitiveCollate() for a the typical use case for
this functionality.  This tests both using IndexBasedSepllChecker and DirectSolrSpellChecker.

> Two new Spelling Parameters were added:
>   - spellcheck.alternativeTermCount - The count of suggestions to return for each query
term existing in the index and/or dictionary.  Presumably, users will want fewer suggestions
for words with docFrequency>0.  Also setting this value turns "on" context-sensitive spell
>   - spellcheck.maxResultsForSuggest - The maximum number of hits the request can return
in order to both generate spelling suggestions and set the "correctlySpelled" element to "false".
 For example, if this is set to 5 and the user's query returns 5 or fewer results, the spellchecker
will report "correctlySpelled=false" and also offer suggestions (and collations if requested).
 Setting this greater than zero is useful for creating "did-you-mean" suggestions for queries
that return a low number of hits.
> I have also included a test using shards.  See additions to DistributedSpellCheckComponentTest.

> In Lucene, can already support this functionality (by passing a null
IndexReader and field-name).  The DirectSpellChecker, however, needs a minor enhancement.
 This gives the option to allow DirectSpellChecker to return suggestions for all query terms
regardless of frequency.

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