NF-NR: A practical normal form for nested relations |
| |
Authors: | Tok-Wang Ling Ling-Ling Yan |
| |
Affiliation: | (1) Dept. of Information Systems and Computer Science, National University of Singapore, 0511 Kent Ridge, Singapore;(2) Present address: Department of Computing Science, University of Alberta, Edmonton, Alberta, Canada |
| |
Abstract: | We propose a normal form for nested relations, called NF-NR, which removes undesirable anomalies from a nested relational database schema. Both functional dependencies and multivalued dependencies are considered. NF-NR reduces to 3NF/4NF if the nested relation considered is actually a flat relation. Especially, NF-NR removes global redundancies among a set of nested relations. Two approaches to NF-NR database design, namely the restructuring rules approach and the ER approach, are discussed. We relate NF-NR to ER-NF, a normal form of ER defined earlier, by defining a simple mapping from an ERD in ER-NF to a set of nested relations in NF-NR. This approach effectively removes ambiguitics and redundancies on a semantic level and hence gives a set of nested relations with clean semantics and yet in good normal form. A set of desirable properties for any normal form for nested relations are described and an evaluation of several existing normal forms is given based on this set of properties. The evaluation shows that NF-NR improves over previously proposed normal forms in various aspects and is a more practical normal form for nested relations. |
| |
Keywords: | Nested relation normal forms Entity-Relationship Approach extended-functional dependency |
本文献已被 SpringerLink 等数据库收录! |
|