E.11. dict_xsyn

E.11.1. 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.

E.11.2. 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, MATCHSYNONYMS=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, MATCHORIG=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;