On redundancy vs dependency preservation in normalization: an information-theoretic study of 3NF

A recently introduced information-theoretic approach to analyzing redundancies in database design was used to justify normal forms like BCNF that completely eliminate redundancies. The main notion is that of an information content of each datum in an instance (which is a number in [0, 1]): the closer to 1, the less redundancy it carries. In practice, however, one usually settles for 3NF which, unlike BCNF, may not eliminate all redundancies but always guarantees dependency preservation. In this paper we use the information-theoretic approach to prove that 3NF is the best normal form if one needs to achieve dependency preservation. For each dependencypreserving normal form, we define the price of dependency preservation as an information-theoretic measure of redundancy that gets introduced to compensate for dependency preservation. This is a numberin the [0, 1] range: the smaller it is, the less redundancy a normal form guarantees. We prove that for every dependency-preserving normal f...

• Type: Conference
• Year: 2006
• Where: PODS
• Authors: Solmaz Kolahi, Leonid Libkin
• Keywords: Database, Dependency Preservation, Guarantees Dependency Preservation, Normal Form, PODS 2006