The Research On Concurrent Control Algorithm In Real-time Cooperative Editing System

Real-time Cooperative Editing System is a very important application tool in the rapidly expanding areas of CSCW, and it allows a group of users to view and edit the same text/graphics/image/multimedia document at the same time from geographically dispersed sites connected by communication networks. The requirements for real-time, distributed and unconstrained collaboration have led us to adopt a full replicated architecture for the storage of shared documents. This paper places emphasis on the concurrent control algorithm of a full replicated architecture adopted RECES.First, according to the characteristics of cooperative editing system, the main problem is the reasonable scheduling on concurrent operations, and the elimination of concurrent conflicts, so as to achieve the consistency requirements of convergence, causality preservation and intention preservation. Then, after analysis on a variety of real-time collaborative editing systems concurrency control algorithms, a comprehensive analysis for already existing popular algorithms is conducted, and the deficiencies of these algorithms are summed up.GOT algorithm is recognized as a more correct algorithm at present, but it doesn't concern about the cursor position and can only work in simple operations, an improved concurrent control algorithm IGOT is designed to solve the deficiencies of GOT, and is more applicable to the actual collaborative editing systems. IGOT solves the problems by the improvement of both the high-level segment and the lower-level segment of GOT. At high-level part, cursor control mechanism is presented to solve the consistency of cursor position; at lower-level, more complex operations are introducted, and the complex operations can be separated into simple operations which are easily scheduled.After the analysis of lower-level segment and high-level segment, the complexity of IGOT algorithm is obtained. In lower-level segment, operational transformation stategy is proved according to the concurrent relation between operations and history buffer, and cursor position stategy is proved according to history buffer and semantics of operations, and the correctness of lower-level algorithm is proved by integrating the two stategies. In high-level segment, operational transformation functions are proved according to semantics and position parameters of between operations, thus the correctness of high-level algorithm is proved.