XML (eXtensible Markup Language) Catalogs are XML documents consisting of catalog entries. Each entry pairs an identifier to another location. OASIS is a not-for-profit consortium, with the mission of advancing open standards. They published the XML catalog standard, version 1.1, in 2005. This standard has two basic use cases:

• To map an external identifier to a URI reference
• To map a URI reference to another URI reference

Here is a sample XML catalog entry:

<public publicId="-//Packt Publishing Limited//Mastering Java 9//EN" uri="https://www.packtpub.com/application-development/mastering-java-9"/>

The complete OASIS XML Catalog standard can be found at the official site: https://www.oasis-open.org/committees/download.php/14809/xml-catalogs.html.