ISO/IEC 13250-3:2007 defines an extensible markup language (XML) vocabulary for interchanging topic maps. The interpretation of the syntax is defined through a mapping from the syntax to the Topic Maps data model defined in ISO/IEC 13250-2.
The vocabulary, known as XML Topic Maps (XTM) 2.0, is not designed to be extended or modified. Ease of human authoring was not a primary design goal, and consequently it is not recommended to edit the syntax directly.
XTM 2.0 is a revision of the XTM 1.0 vocabulary defined in ISO/IEC 13250:2003, which was adopted verbatim from the XML Topic Maps (XTM) 1.0 specification published by TopicMaps.Org in March 2001. The differences between the two versions are described.