→2009-06-15: fix links
Got a working prototype
[http://git.sugarlabs.org/projects/sugar/repos/versionsupport sugar-datastore],[http://git.sugarlabs.org/projects/sugar/repos/versionsupport sugar-toolkit]). It treats each version as a separate object, unrelated to the others - so no topology, no branches. But it's working and the basic user experience (details view allows selecting old versions, changing metadata and resuming them) is there.
The API has been changed to add a version_id in parallel to object_id. This seemed cleanest, but also needs invasive code changes (though most activities will continue to work as-is - the framework (sugar-toolkit) usually handles save/resume for them). Breaking the API is almost unavoidable - see [http://git.sugarlabs.org/projects/versionsupport-project/repos/mainline/blobs/master/API-choosing-notes.txt my API choosing notes] for details. But I noticed that in most cases we want to identify a single version, so we could alter the Python side of the API to do that by default, in a single parameter - e.g. by passing a tuple (object_id, version_id) - instead of always passing around two separate parameters. The few places where we want to identify all versions of an object, we can do that explicitly.