"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, Ronald (September 1977). Multivalued Dependencies and a New Normal Form for Relational Databases(PDF). ACM Transactions on Database Systems. 2 (1): 267. doi:10.1145/320557.320571. Архів оригіналу(PDF) за 29 листопада 2007. Процитовано 1 квітня 2011.
Wu, Margaret S. (March 1992). The Practical Need for Fourth Normal Form. ACM SIGCSE Bulletin. 24 (1): 19—23. 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, Ronald (September 1977). Multivalued Dependencies and a New Normal Form for Relational Databases(PDF). ACM Transactions on Database Systems. 2 (1): 267. doi:10.1145/320557.320571. Архів оригіналу(PDF) за 29 листопада 2007. Процитовано 1 квітня 2011.
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, Ronald (September 1977). Multivalued Dependencies and a New Normal Form for Relational Databases(PDF). ACM Transactions on Database Systems. 2 (1): 267. doi:10.1145/320557.320571. Архів оригіналу(PDF) за 29 листопада 2007. Процитовано 1 квітня 2011.
