F.12. dict_xsyn

F.12. dict_xsyn
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F.12.1. Configuration
F.12.2. 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.12.1. 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.12.2. 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;

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