Gerenciamento Temporal de Versões para Evolução de Esquemas em BDOO

The use of versions has been essential in several database applications, allowing the storage and the handling of different database states. During the schema evolution, versioning is used to preserve all schema versions, as well as their instances. On the other hand, bitemporal database concepts, that incorporate transaction and valid timestamps, provide flexibility to schema evolution mechanism, allowing not only the access to past and future information, but also updates and queries among the different schema versions. In this paper, an analysis of the schema evolution process in object-oriented databases is realized using a temporal versions model. A meta schema structure is defined to store information concerning the states of the evolutionary schema, as well as their classes, attributes and relationships. An implementation proposal is presented, combining specification and manipulation mechanisms including version and time concepts. For the database extension management, two alternatives are defined: multi-pool for the schema versioning and single-pool for the class versioning. Concerning the physical representation, both approaches can be used in the same application.