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Abstract:

Abstract--- The database schemata often experience considerable changes during the development and initial use phases of database systems for advanced applications, such as automated manufacturing 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 non-realtime 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 foundation to define a schema evolution framework. Therefore, we first design a conceptual real-time object-oriented data model, called ROMPP (Realtime Object Model with Performance Polymorphism). 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 (non-real-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 potential benefits of the proposed schema evolution system. Keywords--- Data model, database, envelope/letter classes, letter class hierarchy, object-oriented, performance polymorphism, real-time, schema evolution.

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