Just confirming on your above statement, realizing service.ID or realizing resource.ID in product inventory point out to Service inventory ID or resource inventory ID.
In such case we have to either create service/resource inventory and associate to party/customer prior to creating product inventory
patch product inventory later.(it seems this is correct as per TMF use case)
Is above understanding correct?
Either approach is acceptable, it very much depends on how you want to run your BSS and OSS business - more specifically, how soon do you want to create service/resource instances during the ordering process.