The OASIS XML catalog is a document describing a mapping between external entity references or URI's and locally-cached equivalents.
A file is considered to be an XML Catalog document when it has the namespace "urn:oasis:names:tc:entity:xmlns:xml:catalog" or when its root element name is catalog.
The OASIS 1.1 schema used for these documents is located in ${frameworks}/xml/catalog1.1.xsd, where ${frameworks} is a subdirectory of the Oxygen install directory.