1. Undo in a Web Application Chasen Le Hara BarCamp LA-4 November 4, 2007

2. The Problem Accidents happen Habits happen Data loss sucks http://ickr.com/photos/wvs/141235163/

3. Is undo a solution? Undo can recover deleted data Undo can reverse changes made to data Undo can make a user less fearful

4. How should a user interact with undo?

5. The back button? Used for going to the previous page Back button is for pages, not state Wont work (easily) with AJAX Not readily apparent to the user

6. A proprietary interface Control over when the option appears to users In line with existing instances of undo

7. Undos Scope

8. What should be undoable? Not all actions can be undone Purpose is to recover past data Delete and edit actions should be undoable

9. How many actions should be undoable? No sense in storing undo actions that will never be undone User forgets about action eventually Data must be deleted sometime

10. When should the undo data be deleted? Never is (almost always) not an option My pick: signing out A user is not likely to want to recover data from a previous sign-in session

11. Implementing Undo

12. Database design Make a table where old data can be stored and recovered through undo Focus on the old data, date/time, and metadata about the undo

13. Backend design Pair every delete/edit action with an undo action entry in the undo table Get a copy of the old data into the undo table before deleting/editing When a user undoes an action, use the old data for an insert or update

14. User chooses to delete data Data table Deleted data Undo table User realizes they deleted the wrong data Data table Deleted data Undo table The deletion is undone

15. Other considerations Delete linked data when the undo action is deleted Think about how data affects other data Expose undo metadata through an API, not the old data

16. Demonstration

17. Thanks!

18. Questions?