Object Evolution in Object Databases

Abstract

There are many aspects related to evolution in object-oriented databases. Not all of them have been investigated in sufficient depth. Generally speaking, one can distinguish between evolution of schemas — for example, modifying a class definition — and of instances — for example, the migration of an instance from one class to another. In the latter kind of evolution, an instance modifies its own structure while maintaining the same identity. In this paper we discuss instance evolution in the context of the Chimera object-oriented data model [11, 18]. However, though developed with reference to the Chimera data model, the discussion is applicable to any object-oriented database system. Chimera1 is an object-oriented, deductive, active data model developed as part of ESPRIT Project Idea P6333. Chimera provides all concepts commonly ascribed to object-oriented data models, such as: object identity, complex objects and user-defined operations, classes, inheritance; it provides capabilities for defining deductive rules, that can be used to define views and integrity constraints, to formulate queries, to specify methods to compute derived information; it supports a powerful language for defining triggers.