Section: New Results

A CRDT Supporting Selective Undo for Collaborative Text Editing

Participants : Luc André, Claudia-Lavinia Ignat [contact] .

Selective undo is an important feature in collaborative editors. With selective undo, a user can undo an earlier operation, regardless of when and where the operation was generated. Current systems that support selective undo are subject to two main limitations. Firstly, they only support undo of operations on atomic objects (e.g. characters or un- breakable lines). In the case of string-wise operations such as copy-paste, find-replace or select-delete, users can typically only undo earlier operations character by charac- ter. Secondly, selective undo may lead to undesirable effects. For example, a user first inserts a misspelled word and then makes a correction. The correction depends on the first insertion of the word. It is undesirable to undo the insertion alone and leave the correction behind as a groundless modification. In [15] we proposed a novel consistency maintenance approach relying on a layered commutative replicated data type (CRDT) that supports selective undo of string-wise operations in collaborative editing. This is the first work that manages undesirable effects of undo. Our performance study shows that it provides sufficient responsiveness to the end users.