OutlineEdit as a PyObjC application
The Tiger developer tools includes several Core Data examples, including OutlineEdit which demonstrates how to manage a hierarchical object graph and display said graph in an NSOutlineView.
PyObjC contains a python version of the same application.
The example’s setup.py also demonstrates how to set up a multiple document based application that compiles an Xcode created model file and sets up an Info.plist with several registered document types.