H. Kim, S. Scerri, J. Breslin, S. Decker, and H. Kim. Proceedings of the 2008 International Conference on Dublin Core and Metadata Applications, page 128--137. Berlin, Deutschland, Dublin Core Metadata Initiative, (2008)
J. Tang, H. fung Leung, Q. Luo, D. Chen, and J. Gong. IJCAI'09: Proceedings of the 21st international jont conference on Artifical intelligence, page 2089--2094. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (2009)
T. Gruber, and G. Olsen. Principles of Knowledge Representation and Reasoning: Proceedings of the 4th International Conference (KR '94): Bonn, Germany: 1994, May, 24 - 27, page 258-269. Morgan Kaufmann Publishers, (1994)