I have put together a very simple diagram to describe some core data flows in Project Online / Project Server for actions like opening projects, save a project on a PDP etc. This high level diagram can be seen below:
Click the image to see a larger version.
There are probably some scenarios where this image isn’t 100% accurate but it gives you a good starting point for most core scenarios / data interactions with Project Online and Project Desktop.
I hope that you find it useful – happy to extend it / update it with more Project Online data entities if people find it useful!