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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)
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