This is an introduction of XML catalog.
An XML catalog, which can be physically composed of several catalog entry files, is a logical structure that describes mapping information. A catalog entry file is an xml file that includes a group of catalog entries.
A catalog entry can be used to locate a unified resource identifier (URI) reference for a certain resource such as a dtd file. An external entity's public identifier is used for mapping to the URI reference.
The URI of any system identifier can be ignored.
XML Catalogs are used to make the XML setup more flexible and portable. Using XML Catalogs, you can
Here is an example of a XML Catalog file.
Example 1. An XML Catalog File: catalog-dita.xml.
<?xml version="1.0" ?> <catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog" prefer="public"> <!-- Catalog for DITA --> <!-- DITA DTDs --> <group xml:base="dtd"> <public publicId="-//IBM//DTD DITA Concept//EN" uri="concept.dtd"/> <public publicId="-//IBM//ELEMENTS DITA Concept//EN" uri="concept.mod"/> ... <!-- Demo/Experimental --> <public publicId="-//IBM//DTD DITA Element Reference//EN" uri="demo/elementref/elementref_shell.dtd"/> <public publicId="-//IBM//ELEMENTS DITA Element Reference//EN" uri="demo/elementref/elementref.mod"/> <public publicId="-//IBM//DTD DITA FAQ//EN" uri="demo/faq/faq_shell.dtd"/> <public publicId="-//IBM//ELEMENTS DITA FAQ//EN" uri="demo/faq/faq.mod"/> </catalog>
The Demo/Experimental section in the catalog-dita.xml file is the section to place demo or experimental dtd descriptions. New DITA specialization features can be added in these descriptions. For example, if you want to use the public identifier, -//IBM//DTD SAMPLE//EN, to refer to the file with the pathname dtd/sample/mysample.dtd, put the following catalog entry within the Demo/Experimental section.
<public publicId="-//IBM//DTD SAMPLE//EN" uri="sample/mysample.dtd"/>