Hi Ryan,
You are modelling from inside out (based on a RFC interface) rather than outside in (what data does your resource present?).
In your case you have a parent entity that has appointment entities. You should therefore define both as entities in the model and provide an association between the two. Generate the DPC and then redefine the access method implementations for the parent (get_entity) and child set (get_entityset). Then you can simply read the collection of appointments from a given parent key.
The use of RFC mapping to multiple sets is old school and it can be done but it's not very flexible or non-disruptive.
Check out Andre Fisher's guide here: http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/f0efbaca-45ba-3010-b7bb-8c1c5aa109ab?QuickLink=index&overridelayout=true&58475979909212