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<p><b>Abstract</b>—The 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, we 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. We 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, we 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. We adopt and extend an axiomatic model to express the semantics of ROMPP schema changes. Using manufacturing-control applications, we demonstrate the applicability of ROMPP and the potential benefits of the proposed schema-evolution system.</p>
Data model, database, envelope/letter classes, letter-class hierarchy, object oriented, performance polymorphism, real-time, schema evolution.

E. A. Rundensteiner, L. Zhou and K. G. Shin, "Schema Evolution of an Object-Oriented Real-Time Database System for Manufacturing Automation," in IEEE Transactions on Knowledge & Data Engineering, vol. 9, no. , pp. 956-977, 1997.
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