Semantic foundations of 4NF in relational database design |
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Authors: | Millist W Vincent |
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Affiliation: | (1) School of Computer and Information Science, University of South Australia, Adelaide, Australia 5095 (e-mail: m.vincent@unisa.edu.au) , AU |
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Abstract: | The issue of providing a formal justification for the use of fourth normal form (4NF) in relational database design is investigated.
The motivation and formal definitions for three goals of database design are presented. These goals are the elimination of:
redundancy, key-based update anomalies and fact-based replacement anomalies. It is then shown that, depending on the type
of constraints permitted, either Boyce-Codd normal form (BCNF) or 4NF are the exact conditions needed to ensure most of the
design goals. However, it is also shown that the conditions required to ensure the absence of a particular class of key-based
update anomaly are new normal forms which have not previously been identified. In particular, for the case where the only
constraints are functional dependencies (FDs), it is shown that the required normal form is a new normal form that is stronger
than third normal form (3NF) yet weaker than BCNF. Similarly, in the more general case where both FD and multivalued dependencies
(MVDs) are present, the required normal form is a new normal form that is weaker than 4NF.
Received: 7 July 1995 / 28 December 1998 |
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Keywords: | |
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