A theory of intersection anomalies in relational database schemes

The desirability of acyclic database schemes is well argued in [8] and [13]. For schemas described by multivalued dependencies, acyclicity means that the dependencies do not split each other's left-hand sides and do not form intersection anomalies. In a recent work [4] it is argued that real-world database schemes always meet the former requirement, and in [5] it is shown that any given real-world scheme can be made to satisfy also the latter requirement, after being properly extended. However, the method of elimination of intersection anomalies proposed in [5] is intrinsically nondeterministic—an undesirable property for a design tool. In the present work it is shown that this nondeterminism does not, however, affect the final result of the design process. In addition, we present an efficient deterministic algorithm, which is equivalent to the nondeterministic process of [5]. Along the way a study of intersection anomalies, which is interesting in its own right, is performed.