Use a Start Ad Hoc Event in your business process definition (BPD) to enable end users to start an ad hoc process during the execution of another process.
If you want to enable end users to start an ad hoc process during the execution of another process, you can do so by using a Start Ad Hoc Event in your BPD. For example, you may want to enable end users to cancel an order, determine the status of an order, or perform some other ad hoc function during the normal processing of an order. Because an ad hoc process is run in the context of the regular process instance, it has access to all the data of the regular process instance and can also manipulate the flow of the regular process instance, depending on the logic that you include.