Issues in object-oriented database schemas
Hyoung Joo Kim · 1988
The successful use of database management systems in data-processing applications has created a substantial amount of interest in applying database techniques to such areas as knowledge bases and artificial intelligence (AI), computer-aided design (CAD), and office information systems (OIS). In order to provide the additional semantics necessary to model these new applications, many researchers have adapted the object-oriented programming paradigm to serve a data model. In order to use the object-oriented approach in a database system, it was necessary to add persistence and sharability to the object-oriented programming paradigm. Several database systems based on this approach are under implementation. The object-oriented data models are more powerful than the conventional data models due to the support of inheritance in class hierarchies and composite objects. The notions of inheritance and composite objects are enormously important in supporting new database applications of AI, CAD, and OIS. However, the object-oriented database schema is more complicated than conventional database schemas because both class hierarchy and composite object structures are directed acyclic graphs (DAG). In this dissertation, we examine various issues of object-oriented database schemas: schema evolution, graphics schema editor, schema versioning, DAG rearrangement views, logical design of object-oriented database schema and subclassing. The practical applications of object-oriented databases, such as CAD, AI, OIS, require the ability to dynamically make a wide variety of changes to the database schema. This process is called schema evolution. We establish a consistent and complete framework of schema evolution. Based on our framework, MCC ODBS group implemented a schema manager within their prototype object-oriented database system, ORION. On top of the schema manager of ORION, we implemented a graphical editor PSYCHO. We present a technique that enables users to manipulate schema versions explicitly and maintain schema evolution histories in object-oriented database environments. We also examine a new concept, DAG rearrangement views, which are rearrangements of DAG structures of composites objects and class hierarchies in object-oriented databases. In the latter part of the thesis, we investigate the logical design of object-oriented database schema. Finally, we elaborate on subclassing which is the most frequently used schema change operation.