"A relation schema R* is in fourth normal form (4NF) if, whenever a nontrivial multivalued dependency X 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 (1977. szeptember 1.). „Multivalued Dependencies and a New Normal Form for Relational Databases”. ACM Transactions on Database Systems2 (1), 262–278. o. [2007. november 29-i dátummal az eredetiből archiválva]. DOI:10.1145/320557.320571. (Hozzáférés: 2008. április 26.)
Wu (1992. március 1.). „The Practical Need for Fourth Normal Form”. ACM SIGCSE Bulletin24 (1), 19–23. o. DOI:10.1145/135250.134515.
ibm.com
almaden.ibm.com
"A relation schema R* is in fourth normal form (4NF) if, whenever a nontrivial multivalued dependency X 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 (1977. szeptember 1.). „Multivalued Dependencies and a New Normal Form for Relational Databases”. ACM Transactions on Database Systems2 (1), 262–278. o. [2007. november 29-i dátummal az eredetiből archiválva]. DOI:10.1145/320557.320571. (Hozzáférés: 2008. április 26.)
web.archive.org
"A relation schema R* is in fourth normal form (4NF) if, whenever a nontrivial multivalued dependency X 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 (1977. szeptember 1.). „Multivalued Dependencies and a New Normal Form for Relational Databases”. ACM Transactions on Database Systems2 (1), 262–278. o. [2007. november 29-i dátummal az eredetiből archiválva]. DOI:10.1145/320557.320571. (Hozzáférés: 2008. április 26.)