Enthought Traits is a great framework to build a default UI from a model. Easy to use, powerful, the default case is the one you want most of the time and it does what you expect
But there is no database persistence. In fact, no persistence at all. You have to write the code to save/load your model yourself. Doing that for XML is pretty simple (there is an abstract API which works for any object in your model), so you just need to write one class with, say, 50 lines of code, no matter how complex your model is.
The UI controls are not easy to extend, so if you need something which doesn't come with it, good luck.
The model mentioned above can be implemented in under one hour, another hour to read/write it from/to XML. The graph navigation for the relation will take a couple of days using the canvas widget from Qt.