F.13. dict_xsyn - example synonym full-text search dictionary
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:
-
matchorigcontrols whether the original word is accepted by the dictionary. Default istrue. -
matchsynonymscontrols whether the synonyms are accepted by the dictionary. Default isfalse. -
keeporigcontrols whether the original word is included in the dictionary's output. Default istrue. -
keepsynonymscontrols whether the synonyms are included in the dictionary's output. Default istrue. -
rulesis the base name of the file containing the list of synonyms. This file must be stored in$SHAREDIR/tsearch_data/(where$SHAREDIRmeans the PostgreSQL installation's shared-data directory). Its name must end in.rules(which is not to be included in therulesparameter).
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, 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;