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Using synonyms in Elasticsearch

We create an index with:

  • two filters: synonyms_expand and synonyms_contract
  • two analyzers: synonyms_expand and synonyms_contract
  • three text fields:
    • text_1 uses the synonyms_expand analyzer at index and search time
    • text_2 uses the synonyms_expand analyzer at index time, but the standard analyzer at search time
    • text_3 uses the synonyms_contract analyzer at index and search time

.

curl -XPUT 'http://127.0.0.1:9200/test/?pretty=1'  -d '
{
   "settings" : {
      "analysis" : {
         "filter" : {
            "synonyms_expand" : {
               "synonyms" : [
                  "foo,bar,baz"
               ],
               "type" : "synonym"
            },
            "synonyms_contract" : {
               "expand" : 0,
               "synonyms" : [
                  "foo,bar,baz"
               ],
               "type" : "synonym"
            }
         },
         "analyzer" : {
            "synonyms_expand" : {
               "filter" : [
                  "standard",
                  "lowercase",
                  "stop",
                  "synonyms_expand"
               ],
               "type" : "custom",
               "tokenizer" : "standard"
            },
            "synonyms_contract" : {
               "filter" : [
                  "standard",
                  "lowercase",
                  "stop",
                  "synonyms_contract"
               ],
               "type" : "custom",
               "tokenizer" : "standard"
            }
         }
      }
   },
   "mappings" : {
      "test" : {
         "properties" : {
            "text_1" : {
               "type" : "string",
               "analyzer" : "synonyms_expand"
            },
            "text_2" : {
               "search_analyzer" : "standard",
               "index_analyzer" : "synonyms_expand",
               "type" : "string"
            },
            "text_3" : {
               "type" : "string",
               "analyzer" : "synonyms_contract"
            }
         }
      }
   }
}
'

Create a doc which includes a word in our synonyms list foo:

curl -XPUT 'http://127.0.0.1:9200/test/test/1?pretty=1'  -d '
{
   "text_3" : "foo dog cat",
   "text_2" : "foo dog cat",
   "text_1" : "foo dog cat"
}
'

See what tokens have been stored in each of our fields:

curl -XGET 'http://127.0.0.1:9200/test/test/_search?pretty=1'  -d '
{
   "facets" : {
      "text_3" : {
         "terms" : {
            "field" : "text_3"
         }
      },
      "text_1" : {
         "terms" : {
            "field" : "text_1"
         }
      },
      "text_2" : {
         "terms" : {
            "field" : "text_2"
         }
      }
   },
   "size" : 0
}
'

#    "facets" : {
#       "text_3" : {
#          "other" : 0,
#          "terms" : [
#             {
#                "count" : 1,
#                "term" : "foo"
#             },
#             {
#                "count" : 1,
#                "term" : "dog"
#             },
#             {
#                "count" : 1,
#                "term" : "cat"
#             }
#          ],
#          "missing" : 0,
#          "_type" : "terms",
#          "total" : 3
#       },
#       "text_2" : {
#          "other" : 0,
#          "terms" : [
#             {
#                "count" : 1,
#                "term" : "foo"
#             },
#             {
#                "count" : 1,
#                "term" : "dog"
#             },
#             {
#                "count" : 1,
#                "term" : "cat"
#             },
#             {
#                "count" : 1,
#                "term" : "baz"
#             },
#             {
#                "count" : 1,
#                "term" : "bar"
#             }
#          ],
#          "missing" : 0,
#          "_type" : "terms",
#          "total" : 5
#       },
#       "text_1" : {
#          "other" : 0,
#          "terms" : [
#             {
#                "count" : 1,
#                "term" : "foo"
#             },
#             {
#                "count" : 1,
#                "term" : "dog"
#             },
#             {
#                "count" : 1,
#                "term" : "cat"
#             },
#             {
#                "count" : 1,
#                "term" : "baz"
#             },
#             {
#                "count" : 1,
#                "term" : "bar"
#             }
#          ],
#          "missing" : 0,
#          "_type" : "terms",
#          "total" : 5
#       }

So, text_1 and text_2 have expanded foo into the full synonym list. text_3 has indexed just foo (which is the first synonym in the collapsed list).

Searching on text_1 uses the synonyms_expand analyzer on the query string, so the query below becomes a query for "foo bar baz":

curl -XGET 'http://127.0.0.1:9200/test/test/_search?pretty=1'  -d '
{
   "query" : {
      "match" : {
         "text_1" : "bar"
      }
   },
   "explain" : 1
}
'

# {
#    "hits" : {
#       "hits" : [
#          {
#             "_source" : {
#                "text_3" : "foo dog cat",
#                "text_1" : "foo dog cat",
#                "text_2" : "foo dog cat"
#             },
#             "_score" : 0.26574233,
#             "_index" : "test",
#             "_shard" : 2,
#             "_id" : "1",
#             "_node" : "Yit05d94RgiUwMg9vzMOgw",
#             "_type" : "test",
#             "_explanation" : {
#                "value" : 0.26574233,
#                "details" : [
#                   {
#                      "value" : 0.08858078,
#                      "details" : [
#                         {
#                            "value" : 0.57735026,
#                            "details" : [
#                               {
#                                  "value" : 0.30685282,
#                                  "description" : "idf(docFreq=1, maxDocs=1)"
#                               },
#                               {
#                                  "value" : 1.8815218,
#                                  "description" : "queryNorm"
#                               }
#                            ],
#                            "description" : "queryWeight(text_1:foo), product of:"
#                         },
#                         {
#                            "value" : 0.15342641,
#                            "details" : [
#                               {
#                                  "value" : 1,
#                                  "description" : "tf(termFreq(text_1:foo)=1)"
#                               },
#                               {
#                                  "value" : 0.30685282,
#                                  "description" : "idf(docFreq=1, maxDocs=1)"
#                               },
#                               {
#                                  "value" : 0.5,
#                                  "description" : "fieldNorm(field=text_1, doc=0)"
#                               }
#                            ],
#                            "description" : "fieldWeight(text_1:foo in 0), product of:"
#                         }
#                      ],
#                      "description" : "weight(text_1:foo in 0), product of:"
#                   },
#                   {
#                      "value" : 0.08858078,
#                      "details" : [
#                         {
#                            "value" : 0.57735026,
#                            "details" : [
#                               {
#                                  "value" : 0.30685282,
#                                  "description" : "idf(docFreq=1, maxDocs=1)"
#                               },
#                               {
#                                  "value" : 1.8815218,
#                                  "description" : "queryNorm"
#                               }
#                            ],
#                            "description" : "queryWeight(text_1:bar), product of:"
#                         },
#                         {
#                            "value" : 0.15342641,
#                            "details" : [
#                               {
#                                  "value" : 1,
#                                  "description" : "tf(termFreq(text_1:bar)=1)"
#                               },
#                               {
#                                  "value" : 0.30685282,
#                                  "description" : "idf(docFreq=1, maxDocs=1)"
#                               },
#                               {
#                                  "value" : 0.5,
#                                  "description" : "fieldNorm(field=text_1, doc=0)"
#                               }
#                            ],
#                            "description" : "fieldWeight(text_1:bar in 0), product of:"
#                         }
#                      ],
#                      "description" : "weight(text_1:bar in 0), product of:"
#                   },
#                   {
#                      "value" : 0.08858078,
#                      "details" : [
#                         {
#                            "value" : 0.57735026,
#                            "details" : [
#                               {
#                                  "value" : 0.30685282,
#                                  "description" : "idf(docFreq=1, maxDocs=1)"
#                               },
#                               {
#                                  "value" : 1.8815218,
#                                  "description" : "queryNorm"
#                               }
#                            ],
#                            "description" : "queryWeight(text_1:baz), product of:"
#                         },
#                         {
#                            "value" : 0.15342641,
#                            "details" : [
#                               {
#                                  "value" : 1,
#                                  "description" : "tf(termFreq(text_1:baz)=1)"
#                               },
#                               {
#                                  "value" : 0.30685282,
#                                  "description" : "idf(docFreq=1, maxDocs=1)"
#                               },
#                               {
#                                  "value" : 0.5,
#                                  "description" : "fieldNorm(field=text_1, doc=0)"
#                               }
#                            ],
#                            "description" : "fieldWeight(text_1:baz in 0), product of:"
#                         }
#                      ],
#                      "description" : "weight(text_1:baz in 0), product of:"
#                   }
#                ],
#                "description" : "sum of:"
#             }
#          }
#       ],
#       "max_score" : 0.26574233,
#       "total" : 1
#    },
#    "timed_out" : false,
#    "_shards" : {
#       "failed" : 0,
#       "successful" : 5,
#       "total" : 5
#    },
#    "took" : 3
# }

Searching on text_2 uses the standard analyzer on the query string, so the query below remains a query for "bar". But because text_2 contains all 3 synonyms, we find our doc:

curl -XGET 'http://127.0.0.1:9200/test/test/_search?pretty=1'  -d '
{
   "query" : {
      "match" : {
         "text_2" : "bar"
      }
   },
   "explain" : 1
}
'

# {
#    "hits" : {
#       "hits" : [
#          {
#             "_source" : {
#                "text_3" : "foo dog cat",
#                "text_1" : "foo dog cat",
#                "text_2" : "foo dog cat"
#             },
#             "_score" : 0.15342641,
#             "_index" : "test",
#             "_shard" : 2,
#             "_id" : "1",
#             "_node" : "Yit05d94RgiUwMg9vzMOgw",
#             "_type" : "test",
#             "_explanation" : {
#                "value" : 0.15342641,
#                "details" : [
#                   {
#                      "value" : 1,
#                      "description" : "tf(termFreq(text_2:bar)=1)"
#                   },
#                   {
#                      "value" : 0.30685282,
#                      "description" : "idf(docFreq=1, maxDocs=1)"
#                   },
#                   {
#                      "value" : 0.5,
#                      "description" : "fieldNorm(field=text_2, doc=0)"
#                   }
#                ],
#                "description" : "fieldWeight(text_2:bar in 0), product of:"
#             }
#          }
#       ],
#       "max_score" : 0.15342641,
#       "total" : 1
#    },
#    "timed_out" : false,
#    "_shards" : {
#       "failed" : 0,
#       "successful" : 5,
#       "total" : 5
#    },
#    "took" : 2
# }

Searching on text_3 uses the synonyms_contract analyzer on the query string, so the query below becomes a query for "foo":

curl -XGET 'http://127.0.0.1:9200/test/test/_search?pretty=1'  -d '
{
   "query" : {
      "match" : {
         "text_3" : "bar"
      }
   },
   "explain" : 1
}
'

# {
#    "hits" : {
#       "hits" : [
#          {
#             "_source" : {
#                "text_3" : "foo dog cat",
#                "text_1" : "foo dog cat",
#                "text_2" : "foo dog cat"
#             },
#             "_score" : 0.15342641,
#             "_index" : "test",
#             "_shard" : 2,
#             "_id" : "1",
#             "_node" : "Yit05d94RgiUwMg9vzMOgw",
#             "_type" : "test",
#             "_explanation" : {
#                "value" : 0.15342641,
#                "details" : [
#                   {
#                      "value" : 1,
#                      "description" : "tf(termFreq(text_3:foo)=1)"
#                   },
#                   {
#                      "value" : 0.30685282,
#                      "description" : "idf(docFreq=1, maxDocs=1)"
#                   },
#                   {
#                      "value" : 0.5,
#                      "description" : "fieldNorm(field=text_3, doc=0)"
#                   }
#                ],
#                "description" : "fieldWeight(text_3:foo in 0), product of:"
#             }
#          }
#       ],
#       "max_score" : 0.15342641,
#       "total" : 1
#    },
#    "timed_out" : false,
#    "_shards" : {
#       "failed" : 0,
#       "successful" : 5,
#       "total" : 5
#    },
#    "took" : 1
# }
@plusjade
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plusjade commented Jan 21, 2014

Thank you for this! =D

@byronvoorbach
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byronvoorbach commented Nov 24, 2016

Thanks for this Clinton, nice overview :)

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