The GNA meta-library already has a set of topic codes which anyone who
there is free to use. The codes are of the form
topic;subtopic;subsubtopic
and are therefore easily extendable.
The meta-library is located at
http://uu-gna.mit.edu:8001/uu-gna/meta-library/index.html
The topic list is located at
http://uu-gna.mit.edu:8001/uu-gna/tech/meta-library/users/topics.html
An explanation of coverage codes and why they are necessary is located at
http://uu-gna.mit.edu:8001/uu-gna/tech/meta-library/users/coverage.html