Google Docs like revisioning?

Question

I need to implement similar revisioning history what Google Docs documents have. I'm just wondering how they have implemented revisioning. If you do one change, then that change is saved. Does that mean they have one full copy of document when one change is made to document or is it possible to somehow automatically merge versions from previous versions?

Answer 1

You should probably take a look at MobWrite. I believe this is what Google Docs uses.

Answer 2

You should read Joel Spolsky's blog post about distributed version control systems for a bit of insight into how it is possible to store only the modifications (avoid keeping a full copy of the document for every change).