Question: Instrument vs Part in the Plugin API
In the Plugin API: I am trying to understand the difference between the 'Instrument' object and the "Part" object. And how each relates to the Staff object. There are no properties across the three object-classes that can serve as associative keys. And in the plugin class hierarchy diagram all three of these objects just hang off the tree as individual leaf nodes. However, in exploring property values in actual scores I have arrived at the below Entity-Relationship diagram.
Could anyone confirm or correct my understanding?
Also attached are two files that I represent (a cleaned up) exploration test-bed for this.