Separating compensation concerns and programming them with compensating automata

Abstract

Compensations have been used for decades in areas such as flow management systems, long-lived transactions and more recently in the service-oriented architecture. Since compensations enable the logical reversal of past actions, by their nature they cross-cut other programming concerns. Thus, intertwining compensations with the rest of the system not only makes programs less well-structured, but also limits the expressivity of compensations due to the tight coupling with the system’s behaviour. To separate compensation concerns from the normal forward behaviour of the system, we propose a novel design paradigm in which compensations are programmed separately from the system, and incorporated within a compensation manager following relevant system events and manages compensations. If the system signals the need to be compensated, the manager triggers the execution of compensations on behalf of the system and subsequently returns control to the system. We show that this approach can be used to program a sophisticated real-life case study which existing compensation approaches have difficulty in handling.