<!-- doc/src/sgml/dict-xsyn.sgml -->

<sect1 id="dict-xsyn" xreflabel="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>matchorig</> controls whether the original word is accepted by
     the dictionary. Default is <literal>true</>.
    </para>
   </listitem>
   <listitem>
    <para>
     <literal>matchsynonyms</> controls whether the synonyms are
     accepted by the dictionary. Default is <literal>false</>.
    </para>
   </listitem>
   <listitem>
    <para>
     <literal>keeporig</> controls whether the original word is included in
     the dictionary's output. Default is <literal>true</>.
    </para>
   </listitem>
   <listitem>
    <para>
     <literal>keepsynonyms</> controls whether the synonyms are included in
     the dictionary's output. 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>
   Installing the <literal>dict_xsyn</> extension 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
-----------------------
 {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}
</programlisting>

   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>