Design of relational database schemes by deleting attributes in the canonical decomposition

摘要

We propose a conceptually simple, though technically complex, algorithmic method for designing relational database schemes. Given a specification of attributes and functional dependencies, the method first produces an initial design called “canonical decomposition.” Each relation scheme is based on a class of equivalent left-hand sides of the functional dependencies whereby classes are considered as representing user-defined object schemes. Subsequently the method stepwise deletes abnormal nonprime attributes, finally achieving third-normal form while preserving the dependencies, the overall object structure of the initial design, and the new property of being “strongly normative.” This property formalizes the basic idea that the presence of an abnormal nonprime attribute in a relation scheme constitutes a “forbidden substructure” that can be eliminated because it is adequately represented elsewhere in the database scheme.