J. Sim&\#233;on, and P. Wadler. POPL '03: Proceedings of the 30th ACM SIGPLAN-SIGACT symposium on Principles of programming languages
, 38, page 1--13. New York, NY, USA, ACM Press, (January 2003)
M. Lee, L. Yang, W. Hsu, and X. Yang. CIKM '02: Proceedings of the eleventh international conference on Information and knowledge management
, page 292--299. New York, NY, USA, ACM Press, (2002)