Q: How does Owncloud know if a new file is uploaded? I'm working on an Owncloud app, but I am wondering how Owncloud knows if a new file is uploaded.
Can someone point it out?

A: You're not too clear on what exactly you want to achieve, but to me it sounds like you want your app to get notified whenever a new file is uploaded, is that right?
Then you should take a look at filesystem hooks - preCreate or postCreate is probably for you depending on when you want to react...
