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<sect1 id="unaccent">
<title>unaccent</title>
<indexterm zone="unaccent">
<primary>unaccent</primary>
</indexterm>
<para>
<filename>unaccent</> removes accents (diacritic signs) from a lexeme.
It's a filtering dictionary, that means its output is
always passed to the next dictionary (if any), contrary to the standard
behavior. Currently, it supports most important accents from european
languages.
</para>
<para>
Limitation: Current implementation of <filename>unaccent</>
dictionary cannot be used as a normalizing dictionary for
<filename>thesaurus</filename> dictionary.
</para>
<sect2>
<title>Configuration</title>
<para>
A <literal>unaccent</> dictionary accepts the following options:
</para>
<itemizedlist>
<listitem>
<para>
<literal>RULES</> is the base name of the file containing the list of
translation rules. 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 pair: character_with_accent character_without_accent
<programlisting>
À A
Á A
 A
à A
Ä A
Å A
Æ A
</programlisting>
</para>
</listitem>
</itemizedlist>
<para>
Look at <filename>unaccent.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>unaccent</> and a dictionary <literal>unaccent</>
based on it, with default parameters. You can alter the
parameters, for example
<programlisting>
=# ALTER TEXT SEARCH DICTIONARY unaccent (RULES='my_rules');
</programlisting>
or create new dictionaries based on the template.
</para>
<para>
To test the dictionary, you can try
<programlisting>
=# select ts_lexize('unaccent','Hôtel');
ts_lexize
-----------
{Hotel}
(1 row)
</programlisting>
</para>
<para>
Filtering dictionary are useful for correct work of
<function>ts_headline</function> function.
<programlisting>
=# CREATE TEXT SEARCH CONFIGURATION fr ( COPY = french );
=# ALTER TEXT SEARCH CONFIGURATION fr
ALTER MAPPING FOR hword, hword_part, word
WITH unaccent, french_stem;
=# select to_tsvector('fr','Hôtels de la Mer');
to_tsvector
-------------------
'hotel':1 'mer':4
(1 row)
=# select to_tsvector('fr','Hôtel de la Mer') @@ to_tsquery('fr','Hotels');
?column?
----------
t
(1 row)
=# select ts_headline('fr','Hôtel de la Mer',to_tsquery('fr','Hotels'));
ts_headline
------------------------
<b>Hôtel</b>de la Mer
(1 row)
</programlisting>
</para>
</sect2>
<sect2>
<title>Function</title>
<para>
<function>unaccent</> function removes accents (diacritic signs) from
argument string. Basically, it's a wrapper around
<filename>unaccent</> dictionary.
</para>
<indexterm>
<primary>unaccent</primary>
</indexterm>
<synopsis>
unaccent(<optional><replaceable class="PARAMETER">dictionary</replaceable>,
</optional> <replaceable class="PARAMETER">string</replaceable>)
returns <type>text</type>
</synopsis>
<para>
<programlisting>
SELECT unaccent('unaccent','Hôtel');
SELECT unaccent('Hôtel');
</programlisting>
</para>
</sect2>
</sect1>
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