Semantic Bijectivity and the Uniqueness of Constant-Complement Updates in the Relational Context

Abstract

Within the context of the relational model, a general technique for establishing that the translation of a view update defined by constant complement is independent of the choice of complement is presented. In contrast to previous results, the uniqueness is not limited to order-based updates (those constructed from insertions and deletions), nor is it limited to those well-behaved complements which define closed update strategies. Rather, the approach is based upon optimizing the change of information in the main schema which the view update entails. The only requirement is that the view and its complement together possess a property called semantic bijectivity relative to the information measure. It is furthermore established that a very wide range of views have this property. This results formalizes the intuition, long observed in examples, that it is difficult to find different complements which define distinct but reasonable update strategies.