Database schemata often experience considerable changes during the development and initial use phases of database systems for advanced applications such as manufacturing automation and computer-aided design. An automated schema evolution system can significantly reduce the amount of effort and potential errors related to schema changes. Although schema evolution for nonreal-time databases was the subject of previous research, its impact on real-time database systems remains unexplored. These advanced applications typically utilize object-oriented data models to handle complex data types. However, there exists no agreed-upon real-time object-oriented data model that can be used as a foundation to define a schema-evolution framework. Therefore, the authors first design a conceptual real-time object-oriented data model, called Real-time Object Model with Performance Polymorphism (ROMPP). It captures the key characteristics of real-time applications-namely, timing constraints and performance polymorphism-by utilizing specialization-dimension and letter-class hierarchy constructs, respectively. They then re-evaluate previous (nonreal-time) schema evolution support in the context of real-time databases. This results in modifications to the semantics of schema changes and to the needs of schema change resolution rules and schema invariants. Furthermore, they expand the schema change framework with new constructs-including new schema change operators, new resolution rules, and new invariants-necessary for handling the real-time characteristics of ROMPP.
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