An XML Catalog

<?xml version='1.0'?>
<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">

  <public publicId="-//OASIS//DTD DocBook XML V4.2//EN"
          uri="/share/doctypes/docbook42/xml/docbookx.dtd"/>

  <system systemId="http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
          uri="/share/doctypes/docbook42/xml/docbookx.dtd"/>

  <uri name="http://docbook.org/rng/4.2/docbook.rng"
       uri="schema/relaxng/docbook.rng"/>

</catalog>