F.13. dict_xsyn — example synonym full-text search dictionary #

   F.13.1. Configuration
   F.13.2. Usage

   dict_xsyn (Extended Synonym Dictionary) is an example of an add-on
   dictionary template for full-text search. This dictionary type replaces
   words with groups of their synonyms, and so makes it possible to search
   for a word using any of its synonyms.

F.13.1. Configuration #

   A dict_xsyn dictionary accepts the following options:
     * matchorig controls whether the original word is accepted by the
       dictionary. Default is true.
     * matchsynonyms controls whether the synonyms are accepted by the
       dictionary. Default is false.
     * keeporig controls whether the original word is included in the
       dictionary's output. Default is true.
     * keepsynonyms controls whether the synonyms are included in the
       dictionary's output. Default is true.
     * rules is the base name of the file containing the list of synonyms.
       This file must be stored in $SHAREDIR/tsearch_data/ (where
       $SHAREDIR means the PostgreSQL installation's shared-data
       directory). Its name must end in .rules (which is not to be
       included in the rules parameter).

   The rules file has the following format:
     * Each line represents a group of synonyms for a single word, which
       is given first on the line. Synonyms are separated by whitespace,
       thus:
word syn1 syn2 syn3

     * The sharp (#) sign is a comment delimiter. It may appear at any
       position in a line. The rest of the line will be skipped.

   Look at xsyn_sample.rules, which is installed in
   $SHAREDIR/tsearch_data/, for an example.

F.13.2. Usage #

   Installing the dict_xsyn extension creates a text search template
   xsyn_template and a dictionary xsyn based on it, with default
   parameters. You can alter the parameters, for example
mydb# ALTER TEXT SEARCH DICTIONARY xsyn (RULES='my_rules', KEEPORIG=false);
ALTER TEXT SEARCH DICTIONARY

   or create new dictionaries based on the template.

   To test the dictionary, you can try
mydb=# SELECT ts_lexize('xsyn', 'word');
      ts_lexize
-----------------------
 {syn1,syn2,syn3}

mydb# ALTER TEXT SEARCH DICTIONARY xsyn (RULES='my_rules', KEEPORIG=true);
ALTER TEXT SEARCH DICTIONARY

mydb=# SELECT ts_lexize('xsyn', 'word');
      ts_lexize
-----------------------
 {word,syn1,syn2,syn3}

mydb# ALTER TEXT SEARCH DICTIONARY xsyn (RULES='my_rules', KEEPORIG=false, MATCH
SYNONYMS=true);
ALTER TEXT SEARCH DICTIONARY

mydb=# SELECT ts_lexize('xsyn', 'syn1');
      ts_lexize
-----------------------
 {syn1,syn2,syn3}

mydb# ALTER TEXT SEARCH DICTIONARY xsyn (RULES='my_rules', KEEPORIG=true, MATCHO
RIG=false, KEEPSYNONYMS=false);
ALTER TEXT SEARCH DICTIONARY

mydb=# SELECT ts_lexize('xsyn', 'syn1');
      ts_lexize
-----------------------
 {word}

   Real-world usage will involve including it in a text search
   configuration as described in Chapter 12. That might look like this:
ALTER TEXT SEARCH CONFIGURATION english
    ALTER MAPPING FOR word, asciiword WITH xsyn, english_stem;