Update semantics of relational views

Abstract

A database view is a portion of the data structured in a way suitable to a specific application. Updates on views must be translated into updates on the underlying database. This paper studies the translation process in the relational model. The procedure is as follows: first, a “complete” set of updates is defined such that together with every update the set contains a “return” update, that is, one that brings the view back to the original state; given two updates in the set, their composition is also in the set. To translate a complete set, we define a mapping called a “translator,” that associates with each view update a unique database update called a “translation.” The constraint on a translation is to take the database to a state mapping onto the updated view. The constraint on the translator is to be a morphism. We propose a method for defining translators. Together with the user-defined view, we define a “complementary” view such that the database could be computed from the view and its complement. We show that a view can have many different complements and that the choice of a complement determines an update policy. Thus, we fix a view complement and we define the translation of a given view update in such a way that the complement remains invariant (“translation under constant complement”). The main result of the paper states that, given a complete set U of view updates, U has a translator if and only if U is translatable under constant complement.