Exception handling in BPM

Exception handling is one of the prime aspects of software design which attributes to the robustness of the application. Exception handling gains more significance in BPM space, since exceptions had to be dealt both at a system level and at a business level. Bruce Silver has added one more dimension to exception handling in BPM, in his article, wherein exceptions had to be dealt at the process modeling itself.

The significance of exception handling at a process modeling step cannot be ignored. There is a need to handle ACID transactions in BPM, with a business solution and it has to be captured in the model with business semantics. For instance, a classic example of flight, hotel and rental car booking when deemed as a single atomic transaction cannot always be dealt at a system level. If flight booking and hotel booking are two different applications in two different domains (if flight carrier and hotel are different companies), then system transactions cannot be propagated and even if it seems to be possible, system level locks for transaction may not be possible to be obtained since the whole transaction may exceed beyond days to complete. The ideal way to deal with this situation is to have three distinct transactions as business process and even if one fails the other transactions must be canceled using a business process. If flight booking has been confirmed and if hotel booking transaction fails, then flight booking should also be canceled, wherein flight cancellation must be modeled as a separate business process.

It becomes imperative for a BPM solution to handle system level exceptions gracefully. Since process instances can span across business days, in case of system exceptions the process state has to be persisted and should be able to recover from the state where it was left. This may not be possible always for each and every process instance. Sometimes there is a good chance that a process instance may get into an irrecoverable state. In such scenarios, it may not be desirable for the users to create a new process instance altogether. The alternatives for irrecoverable instances due to system exceptions are few, and one probable solution could be to create a new process instance and associate the application process data with the new instance, and programmatically navigate process the instance to the workflow step where it failed.

Another alternative is to create an exception business process. Any system level exception occurring in any of the application business process would trigger the exception business process, which would notify the user about the exception. Also exception process can notify a repair/admin team about the exception. Having a repair queue of exceptions can help the repair/admin team to get first hand information about the exception without the need for notification from the business users about what had happened. Also, irrecoverable process instances can be dealt internally within the IT team, without burdening the business users.

In my opinion, a BPM solution should handle both business and system exceptions. Handling every exception at a process model level would clutter the process diagram with fine grained details defeating the very purpose of a business process diagram. The need for hour is a finer distinction between business and system exceptions should be made even before a process is set to get modeled. A business exception may not look like an exception at all from a BPMN perspective, since most of the business exception would be handled by a new business process altogether, instead of the intermediate handler event.