INSERTION ANOMALIES AND THE JUSTIFICATION FOR 4NF IN RELATIONAL DATABASES

The issue of providing a formal justification for the use of fourth no rmal form (4NF) in relational database design is investigated. Extendi ng earlier work by other authors that provided formal definitions of a n insertion anomaly in the case of functional dependency (FD) constrai nts, formal definitions are provided for two types of an insertion ano maly for the case when both FD and multivalued dependency (MVD) constr aints are permitted. It is shown that both types of insertion anomaly are equivalent conditions on a relation scheme and a relation scheme i s in 4NF if and only if both anomalies are absent. It is also shown th at another type of insertion anomaly that does not reflect the symmetr ical nature of MVDs is a weaker condition than 4NF.