Lucene/Solr Synonym-Expanding EDisMax Parser

Current version : 1.2.2 (changelog)

Developer

Nolan Lawson

Health On the Net Foundation

License

Apache 2.0.

Summary

Extension of the ExtendedDisMaxQueryParserPlugin that splits queries into a "normal" query and a "synonym" query. This enables proper query-time synonym expansion, with no reindexing required.

This also fixes lots of bugs with how Solr typically handles synonyms using the SynonymFilterFactory.

For more details, read my blog post on the subject.

Getting Started

The following tutorial will set up a working synonym-enabled Solr app using the example/ directory from Solr itself, running in Jetty.

Step 1

Download the latest JAR file depending on your Solr version:

• hon-lucene-synonyms-1.2.2-solr-3.x.jar for Solr 3.4.0, 3.5.0, 3.6.0, 3.6.1, and 3.6.2
• hon-lucene-synonyms-1.2.2-solr-4.0.0.jar for Solr 4.0.0
• hon-lucene-synonyms-1.2.2-solr-4.1.0.jar for Solr 4.1.0

Step 2

Download Solr from the Solr home page. For this tutorial, we'll use Solr 3.6.2. You do not need the sources; the tgz or zip file will work fine.

Step 3

Extract the compressed file and cd to the example/ directory.

Step 4

Now, you need to bundle the hon-lucene-synonyms-*.jar file into webapps/solr.war. Below is a script that will work quite nicely on UNIX systems. Be sure to change the /path/to/my/hon-lucene-synonyms-*.jar part before running this script.

mkdir myjar
cd myjar
jar -xf ../webapps/solr.war 
cp /path/to/my/hon-lucene-synonyms-*.jar WEB-INF/lib/
jar -cf ../webapps/solr.war *
cd ..

Note that this plugin will not work in any location other than the WEB-INF/lib/ directory of the solr.war itself, because of issues with the ClassLoader.

Step 5

Download example_synonym_file.txt and copy it to the solr/conf/ directory (or solr/collection1/conf/ in Solr 4.x).

Step 6

Edit solr/conf/solrconfig.xml (solr/collection1/conf/solrconfig.xml in 4.x) and add these lines near the bottom (before </config>):

<queryParser name="synonym_edismax" class="solr.SynonymExpandingExtendedDismaxQParserPlugin">
  <str name="luceneMatchVersion">LUCENE_36</str>
  <lst name="synonymAnalyzers">
    <lst name="myCoolAnalyzer">
      <lst name="tokenizer">
        <str name="class">solr.StandardTokenizerFactory</str>
      </lst>
      <lst name="filter">
        <str name="class">solr.ShingleFilterFactory</str>
        <str name="outputUnigramsIfNoShingles">true</str>
        <str name="outputUnigrams">true</str>
        <str name="minShingleSize">2</str>
        <str name="maxShingleSize">4</str>
      </lst>
      <lst name="filter">
        <str name="class">solr.SynonymFilterFactory</str>
        <str name="tokenizerFactory">solr.KeywordTokenizerFactory</str>
        <str name="synonyms">example_synonym_file.txt</str>
        <str name="expand">true</str>
        <str name="ignoreCase">true</str>
      </lst>
    </lst>
  </lst>
</queryParser>

Note that you must modify the luceneMatchVersion above to match the <luceneMatchVersion>...</luceneMatchVersion> tag at the beginning of the solr/conf/solrconfig.xml file.

Step 7

Start up the app by running java -jar start.jar. Jetty may print a ClassNotFoundException, but it shouldn't matter.

Step 8

In your browser, navigate to

http://localhost:8983/solr/select/?q=dog&debugQuery=on&qf=text&defType=synonym_edismax&synonyms=true

You should see a response like this:

<response>
  ...
  <result name="response" numFound="0" start="0"/>
  <lst name="debug">
    <str name="rawquerystring">dog</str>
    <str name="querystring">dog</str>
    <str name="parsedquery">
        +(DisjunctionMaxQuery((text:dog)) (((DisjunctionMaxQuery((text:canis)) 
        DisjunctionMaxQuery((text:familiaris)))~2) DisjunctionMaxQuery((text:hound)) 
        ((DisjunctionMaxQuery((text:man's)) DisjunctionMaxQuery((text:best)) 
        DisjunctionMaxQuery((text:friend)))~3) DisjunctionMaxQuery((text:pooch))))
    </str>
    <str name="parsedquery_toString">
        +((text:dog) ((((text:canis) (text:familiaris))~2) (text:hound) 
        (((text:man's) (text:best) (text:friend))~3) (text:pooch)))
    </str>
    <lst name="explain"/>
    <str name="QParser">SynonymExpandingExtendedDismaxQParser</str>
    ...
  </lst>
</response>

Note that the input query dog has been expanded into dog, hound, pooch, canis familiaris, and man's best friend.

Tweaking the results

Boost the non-synonym part to 1.2 and the synonym part to 1.1 by adding synonyms.originalBoost=1.1&synonyms.synonymBoost=1.2:

+((text:dog)^1.1 (((((text:canis) (text:familiaris))~2) (text:hound) 
(((text:man's) (text:best) (text:friend))~3) (text:pooch))^1.2))

Apply a minimum "should" match of 75% by adding mm=75%25:

+((text:dog) ((((text:canis) (text:familiaris))~1) (text:hound) 
(((text:man's) (text:best) (text:friend))~2) (text:pooch)))

Observe how phrase queries are properly handled by using q="dog" instead of q=dog:

+((text:dog) ((text:"canis familiaris") (text:hound) (text:"man's best friend") (text:pooch)))

Gotchas

Keep in mind that you must add defType=synonym_edismax and synonyms=true to enable the parser in the first place.

Also, you must either define qf in the query parameters or defaultSearchField in solr/conf/schema.xml, so that the parser knows which fields to use during synonym expansion.

Query parameters

The following are parameters that you can use to tweak the synonym expansion.

Param	Type	Default	Summary
synonyms	boolean	false	Enable or disable synonym expansion entirely. True if enabled.
synonyms.analyzer	String	null	Name of the analyzer defined in solrconfig.xml to use. (E.g. in the examples, it's myCoolAnalyzer). This must be non-null, if you define more than one analyzer (e.g. for more than one language).
synonyms.originalBoost	float	1.0	Boost value applied to the original (non-synonym) part of the query.
synonyms.synonymBoost	float	1.0	Boost value applied to the synonym part of the query.
synonyms.disablePhraseQueries	boolean	false	True if synonym expansion should be disabled when the user input contains a phrase query (i.e. a quoted query). This option is offered because expansion of phrase queries may be considered non-intuitive to users.
synonyms.constructPhrases	boolean	false	v1.2.2: True if expanded synonyms should always be treated like phrases (i.e. wrapped in quotes). This option is offered in case your synonyms contain lots of phrases composed of common words (e.g. "man's best friend" for "dog"). Only affects the expanded synonyms; not the original query. See issue #5 for more discussion.

Compile it yourself

Download the code and run:

mvn install

Since there are several branches depending on the Solr version, there's also a build script that will git checkout each branch, build it, and put it in the target/s3 direcdtory:

./build_all_versions.sh

Testing

Python-based unit tests are in the test/ directory. You can run them by following the "Getting Started" directions and then running:

nosetests test/

Currently I test against Solr 4.1.

Changelog

• v1.2.2
• Added synonyms.constructPhrases option to fix issue #5
• Added proper handling for phrase slop settings
• v1.2.1
• Added support for Solr 4.1.0 (#4)
• v1.2
• Added support for Solr 4.0.0 (#3)
• v1.1
• Added support for Solr 3.6.1 and 3.6.2 (#1)
• Added "Getting Started" instructions to clarify plugin usage (#2)
• v1.0
• Initial release