A plug-in for the DITA toolkit that enables a taxonomy specialization is available for download at sourceforge.net. Although the plug-in is somewhat experimental, it is being used, and merits mention here.
The URL to access the plug-in is:
http://sourceforge.net/project/showfiles.php?group_id=132728
Here are some simple notes on how to retrieve and install the plug-in.
ant -f demo\thesaurus\install-plugin.xml
The specialization plug-in provides documentation at the relative path of demo\thesaurus\doc and a sample at demo\thesaurus\sample within your base DITA directory.
Broader topic: Taxonomies and subject classification