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<!-- $PostgreSQL: pgsql/doc/src/sgml/dict-xsyn.sgml,v 1.2 2007/12/06 04:12:10 tgl Exp $ -->
<sect1 id="dict-xsyn">
<title>dict_xsyn</title>
<indexterm zone="dict-xsyn">
<primary>dict_xsyn</primary>
</indexterm>
<para>
<filename>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.
</para>
<sect2>
<title>Configuration</title>
<para>
A <literal>dict_xsyn</> dictionary accepts the following options:
</para>
<itemizedlist>
<listitem>
<para>
<literal>keeporig</> controls whether the original word is included (if
<literal>true</>), or only its synonyms (if <literal>false</>). Default
is <literal>true</>.
</para>
</listitem>
<listitem>
<para>
<literal>rules</> is the base name of the file containing the list of
synonyms. This file must be stored in
<filename>$SHAREDIR/tsearch_data/</> (where <literal>$SHAREDIR</> means
the <productname>PostgreSQL</> installation's shared-data directory).
Its name must end in <literal>.rules</> (which is not to be included in
the <literal>rules</> parameter).
</para>
</listitem>
</itemizedlist>
<para>
The rules file has the following format:
</para>
<itemizedlist>
<listitem>
<para>
Each line represents a group of synonyms for a single word, which is
given first on the line. Synonyms are separated by whitespace, thus:
<programlisting>
word syn1 syn2 syn3
</programlisting>
</para>
</listitem>
<listitem>
<para>
The sharp (<literal>#</>) sign is a comment delimiter. It may appear at
any position in a line. The rest of the line will be skipped.
</para>
</listitem>
</itemizedlist>
<para>
Look at <filename>xsyn_sample.rules</>, which is installed in
<filename>$SHAREDIR/tsearch_data/</>, for an example.
</para>
</sect2>
<sect2>
<title>Usage</title>
<para>
Running the installation script creates a text search template
<literal>xsyn_template</> and a dictionary <literal>xsyn</>
based on it, with default parameters. You can alter the
parameters, for example
<programlisting>
mydb# ALTER TEXT SEARCH DICTIONARY xsyn (RULES='my_rules', KEEPORIG=false);
ALTER TEXT SEARCH DICTIONARY
</programlisting>
or create new dictionaries based on the template.
</para>
<para>
To test the dictionary, you can try
<programlisting>
mydb=# SELECT ts_lexize('xsyn', 'word');
ts_lexize
-----------------------
{word,syn1,syn2,syn3}
</programlisting>
but real-world usage will involve including it in a text search
configuration as described in <xref linkend="textsearch">.
That might look like this:
<programlisting>
ALTER TEXT SEARCH CONFIGURATION english
ALTER MAPPING FOR word, asciiword WITH xsyn, english_stem;
</programlisting>
</para>
</sect2>
</sect1>
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