As of SAP Release 4.0B, you can link the process of releasing (approving, or giving the "green light" to) purchase orders to the SAP Business Workflow facility. This is particularly advisable if employees whose normal duties involve tasks other than releasing purchase orders are involved in the release procedure.
The employee is automatically informed if release has to be effected: he or she receives a work item in his or her integrated inbox, which can be directly processed from within the inbox. The release transaction is automatically invoked with the relevant release code when the item is processed.
A precondition for this is that the release procedure for purchase orders has been set up in Customizing for Purchasing. The SAP Business Workflow release procedure for purchase orders is set up in the same way as that for requisitions.