I will attempt to explain the different service provisioning related API using an example.
Assume that our company sells e-link services virtual ethernet connections between two edge routers.
The service order management will receive a service order (TMF-641) which has an orderItem to add one CFS with serviceSpecification "eLink". The service order management will validate the order and create a CFS in the service Inventory (TMF-638).
In the serviceDesign phase the service order management will use the service catalog (TMF-633) to find out how this CFS is designed. The catalog will indicate that this CFS requires two RFS with serviceSpecification eLinkRouterConfig. The service order management will create these RFS in the service inventory (TMF-638). It will also update the CFS with the relationship to the RFS and update the status of the CFS to indicate that the serviceDesign is completed (TMF-638).
On the startDate of the serviceOrder the order management will update the CFS status to indicate that activation is pending. (TMF-638) It will also update the status of the RFS to the same status (TMF-638). When the status of an RFS is pendingActive, the order management will for each RFS collect information from the CFS (using relationships) and Resources (the routers) and will call the router configuration NMS (TMF-640) with this information.
When the NMS confirms the configurations are active on the routers, the service order management updates the status of the RFS to active (TMF-638). When all RFS are active also the CFS is set to active (TMF-638) and the service order is set to completed.
I hope this short story explains the use case sufficiently.