Some results about keys of relational schemas. - Ho Thuan; Le Van Bao (Acta Cybern., 1985)

Translation of Relation Schemes, Balanced Relation Schemes and the Problem of Key Representation. - János Demetrovics; Ho Thuan; Nguyen Xuan Huy; Le Van Bao (J. Inf. Process. Cybern., 1987)

Key and superkey for a closure function. - Le Van Bao; Ho Thuan (Acta Cybern., 1989)