1. Allen, J.F. (1981). An interval-based representation of temporal knowledge. In Proceedings of the Seventh International Joint Conference in Artificial Intelligence (pp. 221–226). Vancouver, British Columbia, Canada: IJCAI.
2. Allen, J.F. (1983). Maintaining knowledge about temporal intervals. Communications of the ACM, 26(11), 832–843.
3. Berners-Lee, T., Hendler, J., & Lassila, O. (2001). The semantic web. Scientific American, May 2001. Retrieved June 19 2001 from http://www.sciam.com/ 2001/0501issue/0501berners-lee.html
4. Bobrow, D., & Winograd, T. (1977). An overview of KRL, a knowledge representation language. Cognitive Science, 1, 263–285.
5. Bobrow, D. G., & Stefik, M. S. (1983). The LOOPS manual. Xerox Corporation