Designing gamma-acyclic database schemes using decomposition and augmentation techniques

Abstract

There are several desirable design properties for relational database schemes, such as lossless join property (LJP), BCNF and 4NF property, and the recently introduced various degrees of acyclicity.

In this paper, a method is given for designing database schemes that enjoy these properties. This method is based on the decomposition algorithm of Fagin, cf. /Ul 82/, and on the surrogate concept, called L-augmentation, of Kandzia and Mangelmann, cf. /KaMa 80/. An L-augmentation suitably enlarges a relation scheme by additional attributes and fd's, such that the resulting relation scheme is ‘equivalent’ to the original one.

The method works for universal relation schemes containing fd's and mvd's. The initial universal relation scheme is changed dynamically by this design method. In each iteration, a surrogate and two new fd's are introduced, followed by a sequence of decomposition steps. The final result is an L-augmentation of the universal relation scheme and a lossless, γ-acyclic 4NF database scheme for the L-augmented relation scheme.

This method can be specialized, such that the number of relation schemes in the database scheme is linear in the number of original attributes.