Topic Maps

have been developed since the early 90's.

are now (since early 2000) standardized as ISO/IEC 13250 and form a part of the SGML family of standards.

are in a separate effort developed as XML Topic Maps at TopicMaps.Org, with XTM 1.0 published in December 2000.

After some turbulences, the XTM 1.0 DTD is now on the track to be appended in ISO/IEC 13250.