Consistent schema version removal: an optimization technique for object-oriented views

Abstract

Powerful solutions enabling interoperability must allow applications to evolve and requirements of shared databases to change, while minimizing such changes on other integrated applications. Several approaches, such as the transparent schema evolution system (TSE) by Ra et al., schema versions by Lautemann, and integrated views by Bertino, have been proposed to make interoperability possible by using object-oriented techniques. These approaches may generate a large number of schema versions over time resulting in an excessive build-up of classes and underlying object instances, not all being necessarily still in use. This results in degradation of system performance due to the view maintenance and the storage overhead costs. In this paper, we address the problem of removing obsolete view schemas. We characterize four potential problems of schema consistency that could be caused by removal of a single derived class. We demonstrate that schema version removal is sensitive to the order in which individual classes are processed, and present a formal dependency model that captures all dependencies between classes as logic clauses and manipulates them to make decisions on class deletions and non-deletions while guaranteeing the consistency of the schema. We have also developed and proven consistent a dependency graph (DG) representation of the formal model. Lastly, we present a cost model for evaluating alternative removal patterns on DG to assure selection of the optimal solution. The proposed techniques have been implemented in our Schema View Removal (SVR) tool. Lastly, we report experimental findings for applying our techniques for consistent schema version removal on the MultiView/TSE system.

Software Language Evolution

“…TSE (Transparent Schema Evolution) also supports a view-based simulation of capacity-increasing changes [Ra and Rundensteiner, 1995b, Crestana-Jensen et al, 2000. Schema changes mapped onto views are expressed in the view definition language MultiView.…”

“…Views are an integral part of many database systems and are commonly used to continuously support different versions of a schema [Liu et al, 1993, 1994, Ra and Rundensteiner, 1995a,b, 1997, Crestana-Jensen et al, 2000, or to support coupled evolution without having to change or recreate the original database [Tresch andScholl, 1993, Brèche et al, 1995]. In modelware, grammarware and XMLware, (editable) views are not widely used, hence their application to coupled evolution is lacking.…”

Lazy modular upgrades in persistent object stores

“…The work on schema or class versioning (e.g., [26,49,22]) considers multiple co-existing versions of a schema or class. The work on object instance evolution (e.g., [8,31]) considers selective transformation of some but not all objects in a class.…”

Dependency Language Representation Using Conceptual Graphs. Autonomic Information Systems

“…Some sources maintain that dependencies are simply first-order logic formulae, or in database terminology, constraints [18], [4], [5]. Others insist that higher-order logic is required to express dependencies.…”