For the real-time mode, which is currently under development in DocSynch, rather new and complex algorithms have to be implemented. They are the results of research about Real-time Collaborative Editing since the year 1989.
Operational Transformation - SIGCE
Go to the special interest group for collaborative editing (SIGCE) as a central station to researchers and insightful papers about the topic. Two good papers are:
- Operational Transformation in Real-Time Group Editors: Issues, Algorithms, and Achievements [pdf] (C. Sun and C. Ellis)
- Achieving convergence, causality preservation and intention-preservation in real-time cooperative editing systems [pdf] (C. Sun et al)
There is a nice presentation of Mr. Sun at Microsoft research (February 2003). The Microsoft website includes a video (Attention: the video gets streamed but is about 230 MB! You should view that page with Internet Explorer and newest Windows Media Player installed).
Proving Transformation Functions
Also, be sure to read Proving Correctness of Transformation Functions in Real-Time Groupware [pdf] and most importantly Achieving Convergence with Operational Transformation in Distributed Groupware Systems [pdf] by A. Imine et al., because they prove Sun's transformation functions to be incorrect (well, in rare cases). They have used a tool to check all possible combinations, so there you can be sure about the results. Here is the software they wrote and used:
They propose correct functions in their paper (that's good, although they do not present exclusion transformation functions for the GOTO algorithm :-(.