A Flexible Approach for Instance Adaptation During Class Versioning

One of the consequences of evolution can be the inability to access objects created using the older schema definition under the new definition and vice versa. Instance adaptation is the conversion of objects to a compatible definition or making objects exhibit a compatible interface. Existing evolution approaches are committed to a particular instance adaptation strategy. This is because changes to the instance adaptation strategy or an attempt to adopt an entirely different strategy would be very costly. This paper proposes a flexible instance adaptation approach for systems employing class versioning to manage evolution. Flexibility is achieved by encapsulating the instance adaptation code in aspects abstractions introduced by aspect-oriented programming to localise cross-cutting concerns. This makes it possible to make cost-effective changes to the instance adaptation strategy. The flexibility of the approach is demonstrated by using two instance adaptation strategies: error handlers and update/backdate methods.