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<chapter id="datatype">

<title id="datatype-title">Data Types</title>

processed in UTF-8, computations will be most efficient if the

server encoding is also UTF-8.

</para>

<para>

<acronym>XML</> (Extensible Markup Language) support is not

just the existance of an <type>xml</type> data type, but a

variety of features supported by a database system. These

capabilities include import/export, indexing, searching,

transforming, and <acronym>XML</> to <acronym>SQL</> mapping.

<productname>PostgreSQL</> supports some but not all of these

<acronym>XML</> capabilities. For an overview of <acronym>XML</>

use in databases, see <ulink

url="http://www.rpbourret.com/xml/XMLAndDatabases.htm"></>.

</para>

<variablelist>

<varlistentry>

<term>Import/Export</term>

<listitem>

<para>

There is no facility for mapping <acronym>XML</> to relational

tables. An external tool must be used for this. One simple way to

export <acronym>XML</> is to use <application>psql</> in

<acronym>HTML</> mode (<literal>\pset format html</>), and convert

the <acronym>XHTML</> output to XML using an external tool.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>Indexing</term>

<listitem>

<para>

<filename>/contrib/xml2</> functions can be used in expression

indexes to index specific <acronym>XML</> fields. To index the

full contents of <acronym>XML</> documents, the full-text indexing

tool <filename>/contrib/tsearch2</> can be used. Of course,

Tsearch2 indexes have no <acronym>XML</> awareness so additional

<filename>/contrib/xml2</> checks should be added to queries.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>Searching</term>

<listitem>

<para>

XPath searches are implemented using <filename>/contrib/xml2</>.

It processes <acronym>XML</> text documents and returns results

based on the requested query.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>Transforming</term>

<listitem>

<para>

<filename>/contrib/xml2</> supports <acronym>XSLT</> (Extensible

Stylesheet Language Transformation).

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>XML to SQL Mapping</term>

<listitem>

<para>

This involves converting <acronym>XML</> data to and from

relational structures. <productname>PostgreSQL</> has no internal

support for such mapping, and relies on external tools to do such

conversions.

</para>

</listitem>

</varlistentry>

</variablelist>

</sect1>

</chapter>