jBPM is based on Graph Oriented Programming (GOP). Basically, GOP specifies a simple state machine that can handle concurrent paths of execution. But in the execution algorithm specified in GOP, all state transitions are done in a single operation in the thread of the client. If you're not familiar with the execution algorithm defined in ???, please read that first. By default, this performing state transitions in the thread of the client is a good approach cause it fits naturally with server side transactions. The process execution moves from one wait state to another wait state in one transaction.

But in some situations, a developer might want to fine-tune the transaction demarcation in the process definition. In jPDL, it is possible to specify that the process execution should continue asynchronously with the attribute async="true". async="true" can be specified on all node types and all action types.