Fourth Normal Form (4NF)

Fourth Normal Form (4NF) - (1) A relation R is in fourth normal form (4NF) if and only if, whenever there exists an MVD in R, say A ->-> B, then all attributes of R are also functionally dependent upon A. In other words, the only dependencies (FDs or MVDs) in R are of the form K -> X (i.e., a functional dependency from a candidate K to some other attribute X). Equivalently, R is in 4NF if it is in BCNF and all MVDs in R are in fact FDs. (2) A table is in 4NF if no row of the table contains two or more independent multivalued facts about an entity.

[Category=Data Quality ]

Source: Larry English, http://www.iaidq.com/main/glossary.shtml , 26-Jan-2009 09:27