Concluding Remarks and Future Work

In this paper we have described an approach to apply reflection to a legacy TP monitor in order to support the implementation of extended transaction models. While the legacy TP monitor already supported a rudimentary form of an open-implementation through the existence of a transaction event facility and interfaces to adjust functionality, we found it lacking a most important feature, namely, the reification of application transaction state and execution behaviors into distinct meta-level objects. We introduced the Reflective Transaction Framework, in which reflection is manifested in a small number of add-on software modules called transaction adapters. Transaction adapters build on the available transaction event and application programming interface facilities of the TP monitor to implement reification and reflection, and provide a meta interface through which users can adjust the behavior of the TP monitor functional component. The Reflective Transaction Framework provides programmers who find the default transaction model insufficient for their applications, the means to reach in to a conventional legacy TP monitor and implement new extended transaction models to meet the requirements specific to their application.

The Reflective Transaction Framework represents a new application of reflective concepts. While there have been papers that discuss various aspects of reflection and classify metalevel reflective architectures from different viewpoints, there are few previous works that apply reflection to legacy systems. One contribution of the Reflective Transaction Framework is that it demonstrates the practicality and usefulness of this new application of reflection to incrementally extend a legacy TP monitor. In general, this requires very little change at the underlying TP monitor. A distinct advantage of this approach is that of reusability. A second, more pragmatic contribution of the Reflective Transaction Framework, is that it provides the first practical method to implement a wide range of extended transaction models on an industrial-grade TP monitor. By doing so, we hope this will enables application developers to draw conclusions from direct experience in applying extended transaction models in real, working environments.

Our current implementation of the Reflective Transaction Framework is implemented on the commercial TP monitor Encina. We are currently in the process of measuring and optimizing the performance of this implementation. In addition, we are working to extend the ideas of the framework to other TP monitors, and to other research challenges in advanced transaction processing, such as semantics-based concurrency control protocols [BPZH95]. It is our hope that this work will not only provide solutions of practical value to these challenging problems, but provide insights into the general application of the notions of reflection and open implementation to legacy systems.