https://en.wikipedia.org/wiki/Topic_map
The topic maps (ISO/IEC 13250) reference model and data model standards are defined independent of any specific serialization or syntax.
TMRM Topic Maps – Reference Model
TMDM Topic Maps – Data Model
Topic Maps API[edit]
A de facto API standard called Common Topic Maps Application Programming Interface (TMAPI) was published in April 2004 and is supported by many Topic Maps implementations or vendors:
TMAPI – Common Topic Maps Application Programming Interface
TMAPI 2.0 Topic Maps Application Programming Interface (v2.0)
http://socialcompare.com/en/comparison/list-of-free-mind-mapping-and-concept-mapping-softwares