[SOLR-2585] Context-Sensitive Spelling Suggestions & Collations

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 4.0-ALPHA
• Fix Version/s: 4.0-ALPHA
• Component/s: spellchecker
• Assignee: James Dyer
• Reporter: James Dyer
• Created: 10/Jun/11 21:44
• Updated: 07/Dec/15 16:22
• Resolved: 23/May/12 15:28

Description

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 suggestions.
• 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, SpellChecker.java 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.

Issue Links

• depends upon: LUCENE-3436 Spellchecker "Suggest Mode" Support
• incorporates: SOLR-3457 Spellchecker always incorrectly spelled
• is related to: SOLR-2555 Always incorrectly spelled with onlyMorePopular enabled