Dear Sachin
only for completeness: by whatever reason: you can use "reference" in standard import.
For inheritance: we only option which I know is "IDOC" .. Reference and inheritance have some clear differences (design etc.): in most cases referencing is not a bad option; inheritance as such has been optimized as well by SAP. PLease check the OCC part, I am not sure but may be inheritance is supported
C.B.