The API uses (optional) optimistic concurrency. So when you write a file, you can specify the expected parent revision, and if the revisions don't match, the op

The API uses (optional) optimistic concurrency. So when you write a file, you can specify the expected parent revision, and if the revisions don't match, the operation will fail. If you want, you can have Dropbox instead just overwrite whatever file is present on the server or write the new file but rename it in the process (e.g. "myfile (1).txt"). This is pretty much all that's possible to do generally for files, since their structure is opaque. One of the ideas behind the Datastore API is to support developers structuring their data in such a way that changes can be merged automatically.