THI, V. Đức. On the connections between relations, relation schemes and keys. Journal of Computer Science and Cybernetics, [S. l.], v. 14, n. 4, p. 60–65, 2016. DOI: 10.15625/1813-9663/14/4/7974. Disponível em: https://vjs.ac.vn/index.php/jcc/article/view/7974. Acesso em: 19 apr. 2024.