View updates in relational databases with an independent scheme

Abstract

A view on a database is a mapping that provides a user or application with a suitable way of looking at the data. Updates specified on a view have to be translated into updates on the underlying database. We study the view update translation problem for a relational data model in which the base relations may contain (indexed) nulls. The representative instance is considered to be the correct representation of all data in the database; the class of views that is studied consists of total projections of the representative instance. Only independent database schemes are considered, that is, schemes for which global consistency is implied by local consistency. A view update can be an insertion, a deletion, or a modification of a single view tuple. It is proven that the constant complement method of Bancilhon and Spyratos is too restrictive to be useful in this context. Structural properties of extension joins are derived that are important for understanding views. On the basis of these properties, minimal algorithms for translating a single view-tuple update are given.