Abstract. The family of functional dependencies plays an important role in the relational database. The main .goal of this paper is to investigate choice functions. They are equivalent descriptions of family of functional dependencies. In this paper, we give some main properties related to the composition of choice functions.T6m t~t. H9 cac phu thuoc ham dong vai tro quan trong trong CO" sO-dir li~u quan h~. Muc Wlu cda cluing toi Ill. nghien C1111 v"ecac ham chon. Cac ham chon Ill. cac mo ta tu'ong dirong cda ho cac phu thuoc ham. Trongbal bao nay chiing tc5itrlnh bay m9t so cac tinh cMt co-bin lien quan dgn cac ham chon.
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