WASET
    L. Ludovic and  R. Daniel and  S-E Tbahriti,   Towards an Extended SQLf: Bipolar Query Language with Preferences .   journal   = {International Journal of Computer and Information Engineering}, [online]. World Academy of Science, Engineering and Technology.
    February 2007, vol. 2(2). 363 - 368
    [viewed 09 May 2024]. Available from: https://publications.waset.org/pdf/11600.