Type Evolution and Instance Adaptation

摘要

Schema evolution support is an important facility for object-oriented database(OODB) systems. While existing OODB systems provide for limited forms of evolution, including modification to the database schema and reorganization of affected instances, we find their support insufficient. Specific deficiencies are (1) the lack of compatibility support for old applications, and (2) the lack of ability to install arbitrary changes upon the schema and database. This paper examines the limitations of existing schemes, and offers a more general framework for specifying and reasoning about the evolution of class definitions and the adaptation of existing, persistent instances to those new definitions.