Collaborative undo/redo model

[ekuiter]

Right now, the editor uses a global linear undo/redo model.

This is not an ideal model for collaboration editing. There are other models described in the literature (i.e., direct selective undo) which may be more suitable. These pose new challenges (such as: when is it actually possible to undo any edit from the history? whose edits have to be rolled back as well?). Also the current implementation of state changes (more or less copied from FeatureIDE) assumes a linear undo model and has to be revised.

Other things to consider:

• when and how to consolidate state changes into an artifact? (e.g., upper limit for undo stack size?)
• undoing/redoing state changes in a feature model may concern referencing configurations (see Configuration editor #13)
• give the user an appropriate UI for undoing/redoing state changes (including a list of undoable commands, or a tree, maybe even a list of commands from other users that can be undone, ... this can be arbitrarily complex)

For example, we could provide a split undo menu that undoes the last (own) state change by default, but that provides a menu in which other state changes may be chosen.