If we use some different relationships than this, will it "break" CSDM or have a negative impact in any way?
I believe there should be some more relationships, especially from application instance to application instance (service instance). Some instances uses another instance. It doesn't depend on it because to me, depends on means if the one it depends on is down, this app is down and that isn't the case. Some functionality may be down. The desired operation may not work but there are likely some workarounds in place to handle it unlike those applications that go down and now you're dead in the water. For instance, many apps may use an authentication app for it to be functional for anyone but if that authentication app is down, the other app still works, you may not be able to access it because authentication is down. It may also still run all of it's background services, it's just the user interface portion is unavailable.
Will using Uses::Used by in this scenario cause a problem?
And since I mentioned it, why is it called a service instance rather than an application instance? Isn't it supposed to represent an instance of the business application? I'll leave that for another post.
