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

Powerful solutions enabling interoperability must allow applications to evo lve and requirements of shared databases to change, while minimizing such c hanges on other integrated applications. Several approaches, such as the tr ansparent schema evolution system (TSE) by Ra et al., schema versions by La utemann, and integrated views by Bertino, have been proposed to make intero perability possible by using object-oriented techniques. These approaches m ay generate a large number of schema versions over time resulting in an exc essive build-up of classes and underlying object instances, not all being n ecessarily 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 f our potential problems of schema consistency that could be caused by remova l of a single derived class. We demonstrate that schema version removal is sensitive to the order in which individual classes are processed, and prese nt a formal dependency model that captures all dependencies between classes as logic clauses and manipulates them to make decisions on class deletions and nondeletions while guaranteeing the consistency of the schema. We have also developed and proven consistent a dependency graph (DG) representatio n of the formal model. Lastly, we present a cost model for evaluating alter native removal patterns on DG to assure selection of the optimal solution. The proposed techniques have been implemented in our Schema View Removal (S VR) tool. Lastly, we report experimental findings for applying our techniqu es for consistent schema version removal on the MultiView/TSE system.