1. European dictionary of skills and competences.
http://www.disco-tools.eu
2. International standard classification of education.
http://www.uis.unesco.org/Education/Pages/international-standardclassification-of-education.aspx
3. International standard classification of occupations.
http://www.ilo.org/public/english/bureau/stat/isco/isco08/index.htm
4. Baader, F., Bürckert, H.-J., Heinsohn, J., Hollunder, B., Müller, J., Nebel, B., Nutt, W., Profitlich, H.-J.: Terminological knowledge representation: a proposal for a terminological logic. In: Description Logics, pp. 120–128 (1991)
5. Baader, F., Calvanese, D., McGuinness, D.L., Nardi, D., Patel-Schneider, P.F. (eds.): The Description Logic Handbook: Theory, Implementation, and Applications. Cambridge University Press, Cambridge (2003)