An operation that creates a subgraph of detached objects, using the PrefetchTree to
delineate the graph boundaries. Target objects can be described by a different set of
descriptors, thus allowing server-to-client conversion to happen in the process.
"Detaches" an object from its context by creating an unattached copy. The copy is
created using target descriptor of this operation that may be different from the
object descriptor passed to this method.