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.
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.
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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