Schema changes in an object-oriented database system

Proper and efficient handling of schema changes is an important aspect of any object-oriented database management system. Clearly, it is desirable for an object-oriented database management system to satisfy as many schema operations as possible. This paper deals with schema changes in ODS; an object-oriented database management system prototype. A brief description of the basic features of ODS along with its storage and indexing models are included to facilitate the treatment. The invariants of the class hierarchy/lattice as well as the rules for resolving ambiguities due to schema changes are discussed. In addition, schema changes handled by ODS are described. Schema modifications are done through the user interface of ODS that provides both a class browser and a programming shell. Versions are supported by ODS in handling both methods and messages. For composite objects name conflicts are handled by considering both superclasses and nesting classes.