DPP — which actual interface type should be used in parallel object's reference?

Parallel implementation type - which actual interface type should be
used in the parallel object's reference?

This is specified as the type_id parameter to the create_object
operation of the GenericFactory interface as inherited by the
ParallelObectManager. Note this type also implies the implementation
type of the part objects (the part version of the interface).

[Reviewers: we could add a property to be used in the criteria property
list per part that would supply a part interface that must be derived
from the parallel implementation type?]

Is the 'normal' use case for type_id to be equal to DP_<iface>Part
interface type? How do you envision type_id being used to create the
individual part objects?