WASET
    Keisuke Nakamura and  Kiyoshi Akama and  Hiroshi Mabuchi,  Extending E-learning systems based on Clause-Rule model.   journal   = {International Journal of Computer and Information Engineering}, [online]. World Academy of Science, Engineering and Technology.
    April 2009, vol. 28(4). 1177 - 1183
    [viewed 20 April 2024]. Available from: https://publications.waset.org/pdf/13786.