The Changes feed is now availabile in the Documents List API, informed Russ Jorgensen over at Google Apps Developer Blog. "This feed makes it easier to detect resources that have changed."
"Currently, clients needing to sync resources between Google Docs and other systems or device often encounter a number of issues detecting changes to resources via the API. Clients typically query for all resources modified after a given date. This date is denoted by the app:edited field of a resource entry. However, this field isn't updated in all cases the client may care about, for instance if a resource is shared. In addition, querying for all resources modified after a given date doesn't produce entries for resources that've been deleted. This leads to very complex implementations of change detection by clients. These complex implementations usually have race conditions, and require a large volume of data to be exchanged with the API," Jorgensen said.
"The Changes feed simplifies this process by providing resource entries only for changed resources. If a resource occurs in the Changes feed at all, the occurrence indicates a change to the resource. Once all changes are consumed, clients can store an identifier of the last change consumed. This identifier is called a changestamp. Future queries to the Changes feed with a changestamp will only return changes occurring after the given changestamp," explained Jorgensen.
To start using the Changes feed, make an authorized HTTP GET request to the following URI: https://docs.google.com/feeds/default/private/changes.
[Source: Google Apps Developer Blog]