SCHEMA EVOLUTION OF AN OBJECT-ORIENTED REAL-TIME DATABASE SYSTEM FOR MANUFACTURING AUTOMATION

The database schemata often experience considerable changes during the development and initial use phases of database systems for advanced a pplications such as manufacturing automation and computer-aided design . An automated schema-evolution system can significantly reduce the am ount of effort and potential errors related to schema changes. Althoug h schema evolution for nonreal-time databases was the subject of previ ous research, its impact on real-time database systems remains unexplo red. These advanced applications typically utilize object-oriented dat a models to handle complex data types. However, there exists no agreed -upon real-time object-oriented data model that can be used as a found ation to define a schema-evolution framework. Therefore, we first desi gn a conceptual real-time object-oriented data model, called Real-time Object Model with Performance Polymorphism (ROMPP). It captures the k ey characteristics of real-time applications-namely, timing constraint s and performance polymorphism-by utilizing specialization-dimension a nd letter-class hierarchy constructs, respectively. We then re-evaluat e previous (nonreal-time) schema-evolution support in the context of r eal-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 resolut ion rules, and new invariants-necessary for handling the real-time cha racteristics of ROMPP. We adopt and extend an axiomatic model to expre ss the semantics of ROMPP schema changes. Using manufacturing-control applications, we demonstrate the applicability of ROMPP and the potent ial benefits of the proposed schema-evolution system.