[Solr Wiki] Update of "SpellCheckingAnalysis" by GrantIngersoll

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The following page has been changed by GrantIngersoll:
http://wiki.apache.org/solr/SpellCheckingAnalysis

New page:
= Introduction =

Analysis is a very important factor in spell checking.  Stemming and other techniques that change tokens is not recommended since it will result in giving stems as suggestions.  Instead, you should use a very minimal tokenization/analysis process like the !StandardAnalyzer or even the !WhitespaceTokenizer plus a simple lower casing filter and a filter that removes apostrophes and the like.  As with most things in search, there are always tradeoffs and you should evaluate the results in your application.

That being said, a common configuration for spell checking is:

{{{
<fieldType name="spell" class="solr.TextField" positionIncrementGap="100">
  <analyzer type="index">
    <tokenizer class="solr.StandardTokenizerFactory"/>
    <filter class="solr.StopFilterFactory" ignoreCase="true" words="stopwords.txt"/>
    <filter class="solr.StandardFilterFactory"/>
    <filter class="solr.RemoveDuplicatesTokenFilterFactory"/>
  </analyzer>
  <analyzer type="query">
    <tokenizer class="solr.StandardTokenizerFactory"/>
    <filter class="solr.SynonymFilterFactory" synonyms="synonyms.txt" ignoreCase="true" expand="true"/>
    <filter class="solr.StopFilterFactory" ignoreCase="true" words="stopwords.txt"/>
    <filter class="solr.StandardFilterFactory"/>
    <filter class="solr.RemoveDuplicatesTokenFilterFactory"/>
  </analyzer>
</fieldType>
}}}

Use a <copyField> to divert your main text fields to the spell field and then configure your spell checker to use the "spell" field to derive the spelling index.