ItemAtPath is only intended to work with (return) Locatable objects but we obviously
need to support other Reference Model attributes using paths as well such as
context/health_care_facility and items[at0009]/value. Do we need to change ItemAtPath
to return an Object rather than LOCATABLE or provide a different method for retrieving
DataValue objects such as ValueAtPath? Providing support for returning DataValue objects
will cover a fair amount of the querying requirements but there may still be objects
that are not a DataValue such as PARTY_PROXY or OBJECT_REF.