XML catalog

XML catalogs provide mapping information that maps an external entity in an XML document to the actual location of the document being referenced. You can use a catalog to redirect mappings for an external entity, such as a DTD or XML file, to a different location.

For example, if your XML document is constrained by a DTD that is located on the Internet, and you are working without an Internet connection, you can redirect the reference to a local copy of the DTD. You can then validate your XML document without an Internet connection. Alternatively, you can use XML catalogs to switch between different versions of the DTD.