elasticsearch: can I defined synonyms with boost?

Question

Let's say A, B, C are synonyms, I want to define B is "closer" to A than C

so that when I search the keyword A, in the searching results, A comes the first, B comes the second and C comes the last.

Any help?

Answer 1

There is no search-time mechanism (as of yet) to differentiate between matches on synonyms and source field. This is because, when indexed, a field's synonyms are placed into the inverted index alongside the original term, leaving all words equal.

This is not to say however that you cannot do some magic at index time to glean the information you want.

Create an index with two analyzers: one with a synonym filter, and one without.

PUT /synonym_test/
{
settings : {
  analysis : {
    analyzer : {
      "no_synonyms" : {
        tokenizer : "lowercase"
      },
      "synonyms" : {
        tokenizer : "lowercase",
        filter : ["synonym"]
      }
     },
     filter : {
       synonym : {
         type : "synonym",
         format: "wordnet",
         synonyms_path: "prolog/wn_s.pl"
        }
      }
   }
  }
}

Use a multi-field mapping so that the field of interest is indexed twice:

PUT /synonym_test/mytype/_mapping
{
   "properties":{
     "mood": {
       "type": "multi_field",
       "fields" : {
          "syn" : {"type" : "string", "analyzer" : "synonyms"},
          "no_syn" : {"type" : "string", "analyzer" : "no_synonyms"}
       }
     }
   }

}

Index a test document:

POST /synonym_test/mytype/1
{
  mood:"elated"
}

At search time, boost the score of hits on the field with no synonymn.

GET /synonym_test/mytype/_search
{
  query: {
    bool: {
      should: [
          { match: { "mood.syn" : { query: "gleeful", "boost": 3 } } },
          { match: { "mood.no_syn" : "gleeful" } }
      ]
    }
  }

}

Results in _score":0.2696457

Searching for the original term returns a better score:

GET /synonym_test/mytype/_search
{
  query: {
    bool: {
      should: [
          { match: { "mood.syn" : { query: "elated", "boost": 3 } } },
          { match: { "mood.no_syn" : "elated" } }
      ]
    }
  }

}

Results in: _score":0.6558018,"