The Open for Business Workflow Engine is based on the WfMC and OMG specifications. The Workflow Engine is a member of the Services Framework, and is tightly integrated with the Entity Engine. It uses the entities found in entitymodel_workflow.XML for definition information and entitymode_workeffort for runtime storage. All changes to a process or activity are persisted real-time. Therefore, the engine does not run in a thread, it is simply a group of APIs and common objects which handle the flow. When a change to the workflow is made, the engine then processes that change. When finished, the engine returns. Hence, if the application does crash, or the system reboots, the workflow will continue right where it left off upon restart.
The Workflow Engine is not designed for processing flow of a web site. This is a common misconception. Web site flow is controlled by the Control Servlet. Workflow is the processing of manual and automatic activities to fulfill a specific goal.
OFBiz Workflow Engine uses XPDL as its process definition language.