Revisiting the Behavior of Fault and Compensation Handlers in WS-BPEL

When automating work, it is often desirable to compensate completed work by undoing the work done by one or more activities. In the context of workflow, where compensation actions are defined on nested ’scopes’ that group activities, this requires a model of nested compensation–based transactions. The model must enable the automatic determination of compensation order by considering not only the nesting of scopes but also the control dependencies between them. The current standard for Web services workflows, Business Process Execution Language for Web Services (WS-BPEL), has such compensation capabilities. In this paper, we show that the current mechanism in WS-BPEL shows compensation processing anomalies, such as neglecting control link dependencies between nested non-isolated scopes. We then propose an alternate approach that through elimination of default handlers as well as the complete elimination of termination handlers not only removes those anomalies but also relaxes current WS-BPEL restrictions on control links. The result is a new and deterministic model for handling default compensation for scopes in structures where: (1)both fault handling and compensation handling are present and (2)the relationships between scopes include both structured nesting and graph–based links.