# Dạng chuẩn 4

1. ^ "A relation schema R* is in fourth normal form (4NF) if, whenever a nontrivial multivalued dependency X $\twoheadrightarrow$ Y holds for R*, then so does the functional dependency X → A for every column name A of R*. Intuitively all dependencies are the result of keys." Fagin, Ronald (September năm 1977). “Multivalued Dependencies and a New Normal Form for Relational Databases”. ACM Transactions on Database Systems 2 (1): 267. doi:10.1145/320557.320571.