Rafael Calvo wrote in
this thread about automatic categorization and he also wrote a paper:
"Williams K., R. A. Calvo and D. Bell. Automatic Categorization of Questions for a Mathematics Education Service. Artificial Intelligence in Education Conference. Sydney, Australia. July 2003"
It can be found here:
http://www.weg.ee.usyd.edu.au/people/rafa/papers/
/Håkan
