THUẦN, Hồ; HÀ, Hồ Cẩm. Relational algebra and a point of view for using null value in a fuzzy database model. <b>Journal of Computer Science and Cybernetics</b>, <i>[S. l.]</i>, v. 17, n. 4, p. 1–10, 2012. DOI: 10.15625/1813-9663/17/4/2285. Disponível em: https://jcc.vast.vn/jcc/article/view/2285. Acesso em: 4 nov. 2025.