Semantics and implementation of schema evolution in object-oriented databases
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ICDE '95 Proceedings of the Eleventh International Conference on Data Engineering
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ICDE '96 Proceedings of the Twelfth International Conference on Data Engineering
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VLDB '92 Proceedings of the 18th International Conference on Very Large Data Bases
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ECOOP '91 Proceedings of the European Conference on Object-Oriented Programming
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ER '92 Proceedings of the 11th International Conference on the Entity-Relationship Approach: Entity-Relationship Approach
Consistent Schema Version Removal: An Optimization Technique for Object-Oriented Views
IEEE Transactions on Knowledge and Data Engineering
CASCON '96 Proceedings of the 1996 conference of the Centre for Advanced Studies on Collaborative research
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We have developed the Transparent Schema Evolution (TSE) system that, simulating schema evolution using object-oriented views, allows for the interoperability of applications with diverse and even changing requirements. TSE relieves users of the risk of making existing application programs obsolete when run against the modified schema, because the old view schema is maintained while a new view schema is generated to capture the changes desired by the user. However, TSE may be generating a large number of schema versions (object-oriented view schemata) over time, resulting in an excessive built-up of classes and underlying object instances - some of which may potentially no longer be in use. In this paper, we propose to solve this problem by developing techniques for effective and consistent schema removal. First, we characterize four potential problems of schema consistency that could be caused by removal of a single virtual class; and then outline our solution approach for each of these problems. Second, we demonstrate that view schema removal is sensitive to the order in which individual classes are processed. Our solution to this problem is the development of a dependency graph model for capturing the class relationships, used as a foundation for selecting among removal sequences. Designed to optimize the performance of the TSE system by effective schema version removal, the proposed techniques will enable more effective interoperability among evolving software applications.