Dataspaces and sub-region mapping

Hi, I have a server which own as Ram_dataspace and dishes it out to client's by using sub-rm attachments.

If I pass back to the client the Dataspace_capability for the sub-rm, am I correct in saying that the client cannot get to the physical address of the mapped region since this is a Dataspace not a Ram_dataspace? This this case I'd need to pass it back explicitly as an extra param.

Also, can you clarify the difference between Dataspace and Ram_dataspace and how you can convert (if at all) between the two?

Thanks Daniel