A model of schema versions for object-oriented databases based on the concept of rich base schema

Abstract

In this paper, we propose a model of schema versions for object-oriented databases called RiBS. At the heart of this model is the concept of the rich base schema called (RiBS). In our model, each schema version is in the form of a class hierarchy view over one base schema, called RiBS, which has richer schema information than any existing schema version in the database. Users are supposed to be concerned only with schema versions. Direct schema updates on schema versions are allowed, and their effects are, if necessary, automatically propagated to RiBS. We first describe the structural part of the model and then introduce a set of invariants that should always be satisfied by structural parts. As the third element of our model, we give a set of schema update operations, the semantics of which are defined, so as to preserve all the invariants. Another contribution of this paper is the work on schema-version-merging within the RiBS model. We identify several conflicts in schema-version-merging, and then provide a semi-automatic schema-version-merging algorithm to resolve these conflicts. This algorithm is semi-automatic in the sense that it requires minimal user involvement during schema-version-merging.