A process definition XML file implements a process template that serves as the foundation for initiating business processes. Therefore, it's crucial to understand how to implement and develop a process template, detailed steps of which are outlined in the following interaction.
In addition to employing Java-based methods to implement the business logic for process actions (as mentioned in the interaction), it's also possible to use methods grounded on scripting languages. Detailed information about this can be briefly found on our help portal page, Support for Scripts in Business Process, or extensively covered in our expert deep dive live session: Scripting Support in SAP Commerce Cloud.