Corrective Evolution of Adaptable Process Models

Modeling business processes is a complex and time-consuming task, which can be simplified by allowing process instances to be structurally adapted at runtime, based on context (e.g., by adding or deleting activities). The process model then no longer needs to include a handling procedure for every exception that can occur. Instead, it only needs to include the assumptions under which a successful execution is guaranteed. If a design-time assumption is violated, the exception handling procedure matching the context is selected at runtime. However, if runtime structural adaptation is allowed, the process model may later need to be updated based on the logs of adapted process instances. Evolving the process model is necessary if adapting at run-time is too costly, or if certain adaptations fail and should be avoided. An issue that is insufficiently addressed in the previous work on process evolution is how to evolve a process model and also ensure that the evolved process model continues to achieve the goal of the original model. We refer to the problem of evolving a process model based on selected instance adaptations, such that the evolved model satisfies the goal of the original model, as corrective evolution. Automated techniques for solving the corrective evolution problem are necessary for two reasons. First, the more complex a process model is, the more difficult it is to be changed manually. Second, there is a need to verify that the evolved model satisfies the original goal. To develop automated techniques, we first formalize the problem of corrective evolution. Since we use a graph-based representation of processes, a key element in our formal model is the notion of trace. When plugging an instance adaptation at a particular point in the process model, there can be multiple paths in the model for reaching this point. Each of these paths is uniquely identified by a trace, i.e., a recording of the activities executed up to that point. Depending on traces, an instance adaptation can be used to correct the process model in three different ways. A correction is strict if the adaptation should be plugged in on a precise trace, relaxed if on all traces, and relaxed with conditions if on a subset of all traces. The choice is driven by competing concerns: the evolved model should not introduce untested behavior, but it should also remain understandable. Using our formal model, we develop automated techniques for solving the corrective evolution problem in two cases. The first case is also the most restrictive, when all corrections are strict. This case does not require verification, since the process model and adaptations are assumed to satisfy the goal, as long as the adaptations are applied on the corresponding traces. The second case is when corrections are either strict or relaxed. This second case requires verification, and for this reason we develop an automated technique based on planning. We implemented the two automated techniques as tools, which are integrated into a common toolkit. We used this toolkit to evaluate the tradeoffs between applying strict and relaxed corrections on a scenario built on a real event log.