In this paper we describe our experience applying the concepts of reflection to a legacy transaction processing (TP) monitor in order to support the implementation of extended transaction models. In the past ten years, numerous extended transaction models have been proposed to address the challenges posed by new advanced applications. Few practical implementations of these extended transaction models exist and none are being used in a commercial TP monitor. We believe the reason for this state of affairs is that the interface and functionality of commercial TP monitors is "locked in" to a fixed transaction model. We have developed the Reflective Transaction Framework as a practical method to implement extended transaction models on a commercial TP monitor. The design of our framework is based on the principles of computational reflection, and in particular open implementation.

Refci is an extensible reflective language based on the reflective tower model. The Refci interpreter procedures are reifiable, first-class objects, and user programs can directly modify the interpreter by extending them. This allows user code to be run directly as part of, and at the level of, the interpreter. By installing a modified or extended interpreter, user programs can modularly extend the language and implement debugging aids. We present the extensible first-class interpreter and give examples of its use. Examples include stepping, breakpoints, and interrupts. We show how the reflective tower, modeled by the metacontinuation, maintains the proper level of interpretation when running an interpreter containing both system code and user code.