Daiga,
Without BPM in the PI system, it will be required to build more interfaces, but shall be still technically feasible:
- The first integration flow with async/sync bridge: asynchronous REST sender in polling mode (to call the service GetPackageInfo) to synchronous REST receiver (to call the service GetPackage) and to the asynchronous SAP receiver. Async/sync bridging can be implemented using SAP standard adapter modules - for example, check the blog Bridges Construction Site (1/3): Asynchronous - synchronous bridge.;
- The second integration flow: asynchronous SAP sender (outcome of processing in SAP) to asynchronous REST receiver (to call the service PachageRespons).
Regards,
Vadim