Retrieving document changes

I have been thinking through using an Event Sourcing pattern to control user/group/role permissions for various hosted services that I develop.

Before making the investment, I wanted to find out if there’s an API way for a dependent hosted service to subscribe to that when polled, anything that has changed within document(s) can be downloaded and worked with on the dependent application’s side.

A good reference of what I’m doing may be using google docs and setting up users within the org that can utilize google docs. google docs and the settings site(s) are two different systems, but they work in unison to each other.