Synonym Dictionary

Updated on 2024-09-30 GMT+08:00

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A synonym dictionary is used to define, identify, and convert synonyms of tokens. Phrases are not supported (use the thesaurus dictionary in Thesaurus Dictionary).

Examples

A synonym dictionary can be used to overcome linguistic problems, for example, to prevent an English stemmer dictionary from reducing the word "Paris" to "pari". It is enough to have a Paris paris line in the synonym dictionary and put it before the english_stem dictionary.

      
       
         
         SELECT * FROM ts_debug('english', 'Paris');
   alias   |   description   | token |  dictionaries  |  dictionary  | lexemes 
-----------+-----------------+-------+----------------+--------------+---------
 asciiword | Word, all ASCII | Paris | {english_stem} | english_stem | {pari}
(1 row)

CREATE TEXT SEARCH DICTIONARY my_synonym (
    TEMPLATE = synonym,
    SYNONYMS = my_synonyms,
    FILEPATH =   'obs://bucket01/obs.example.com accesskey=xxxxx secretkey=xxxxx region=eu-west-101'
);

ALTER TEXT SEARCH CONFIGURATION english
    ALTER MAPPING FOR asciiword
    WITH my_synonym, english_stem;

SELECT * FROM ts_debug('english', 'Paris');
   alias   |   description   | token |       dictionaries        | dictionary | lexemes 
-----------+-----------------+-------+---------------------------+------------+---------
 asciiword | Word, all ASCII | Paris | {my_synonym,english_stem} | my_synonym | {paris}
(1 row)

SELECT * FROM ts_debug('english', 'paris');
   alias   |   description   | token |       dictionaries        | dictionary | lexemes 
-----------+-----------------+-------+---------------------------+------------+---------
 asciiword | Word, all ASCII | Paris | {my_synonym,english_stem} | my_synonym | {paris}
(1 row)

ALTER TEXT SEARCH DICTIONARY my_synonym ( CASESENSITIVE=true);

SELECT * FROM ts_debug('english', 'Paris');
   alias   |   description   | token |       dictionaries        | dictionary | lexemes 
-----------+-----------------+-------+---------------------------+------------+---------
 asciiword | Word, all ASCII | Paris | {my_synonym,english_stem} | my_synonym | {paris}
(1 row)

SELECT * FROM ts_debug('english', 'paris');
   alias   |   description   | token |       dictionaries        | dictionary | lexemes 
-----------+-----------------+-------+---------------------------+------------+---------
 asciiword | Word, all ASCII | Paris | {my_synonym,english_stem} | my_synonym | {pari}
(1 row)

        

      
     

The full name of the synonym dictionary file is my_synonyms.syn, and the dictionary is stored in 'obs://bucket01/obs.example.com accesskey=xxxxx secretkey=xxxxx region=eu-west-101'. For details about the syntax and parameters for creating a synonym dictionary, see CREATE TEXT SEARCH DICTIONARY.

An asterisk (*) can be placed at the end of a synonym in the configuration file. This indicates that the synonym is a prefix. The asterisk is ignored when the entry is used in to_tsvector(), but when it is used in to_tsquery(), the result will be a query item with the prefix match marker (see Manipulating Queries).

Assume that the content in the dictionary file synonym_sample.syn is as follows:

      
         postgres        pgsql
postgresql      pgsql 
postgre pgsql 
gogle   googl 
indices index*

Create and use a dictionary.

      
       
         
         CREATE TEXT SEARCH DICTIONARY syn (
    TEMPLATE = synonym,
    SYNONYMS = synonym_sample
);

SELECT ts_lexize('syn','indices');
 ts_lexize 
-----------
 {index}
(1 row)

CREATE TEXT SEARCH CONFIGURATION tst (copy=simple);

ALTER TEXT SEARCH CONFIGURATION tst ALTER MAPPING FOR asciiword WITH syn;

SELECT to_tsvector('tst','indices');
 to_tsvector 
-------------
 'index':1
(1 row)

SELECT to_tsquery('tst','indices');
 to_tsquery 
------------
 'index':*
(1 row)

SELECT 'indexes are very useful'::tsvector;
            tsvector             
---------------------------------
 'are' 'indexes' 'useful' 'very'
(1 row)

SELECT 'indexes are very useful'::tsvector @@ to_tsquery('tst','indices');
 ?column? 
----------
 t
(1 row)

        

      
     