Synonym Dictionary

A Synonym dictionary is used to define, identify, and convert synonyms of a token. Phrases are not supported. Synonyms of phrases can be defined in a Thesaurus dictionary. For details, see 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', define a Paris paris line in the Synonym dictionary and put it before the english_stem dictionary.

  postgres=# SELECT * FROM ts_debug('english', 'Paris');
     alias   |   description   | token |  dictionaries  |  dictionary  | lexemes
  -----------+-----------------+-------+----------------+--------------+---------
   asciiword | Word, all ASCII | Paris | {english_stem} | english_stem | {pari}
  (1 row)
  
  postgres=# CREATE TEXT SEARCH DICTIONARY my_synonym (
      TEMPLATE = synonym,
      SYNONYMS = my_synonyms,
      FILEPATH = 'file:///home/dicts/'
  );
  
  postgres=# ALTER TEXT SEARCH CONFIGURATION english
      ALTER MAPPING FOR asciiword
      WITH my_synonym, english_stem;
  
  postgres=# 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)
  
  postgres=# 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)
  
  postgres=# ALTER TEXT SEARCH DICTIONARY my_synonym ( CASESENSITIVE=true);
  
  postgres=# 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)
  
  postgres=# 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 the /home/dicts/ directory of the current database primary node. For details about the syntax and parameters for creating an Ispell dictionary, see ALTER 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.

  postgres=# CREATE TEXT SEARCH DICTIONARY syn (
      TEMPLATE = synonym,
      SYNONYMS = synonym_sample
  );
  
  postgres=# SELECT ts_lexize('syn','indices');
   ts_lexize
  -----------
   {index}
  (1 row)
  
  postgres=# CREATE TEXT SEARCH CONFIGURATION tst (copy=simple);
  
  postgres=# ALTER TEXT SEARCH CONFIGURATION tst ALTER MAPPING FOR asciiword WITH syn;
  
  postgres=# SELECT to_tsvector('tst','indices');
   to_tsvector
  -------------
   'index':1
  (1 row)
  
  postgres=# SELECT to_tsquery('tst','indices');
   to_tsquery
  ------------
   'index':*
  (1 row)
  
  postgres=# SELECT 'indexes are very useful'::tsvector;
              tsvector
  ---------------------------------
   'are' 'indexes' 'useful' 'very'
  (1 row)
  
  postgres=# SELECT 'indexes are very useful'::tsvector @@ to_tsquery('tst','indices');
   ?column?
  ----------
   t
  (1 row)