Real-time Collaborative Design System Synchronization Issues

Real-time collaborative systems are representative groupware tools in the area of CSCW. They allow multiple users to view and edit the same document at the same time through an interconnected network. As a kind of distributed system that supports human-computer interaction, real-time collaborative systems should be highlighted in practical implementation.When we are developing a real-time collaborative system, three requirements of real-time, distribution and unconstraint are to be fulfilled. Because of the concurrent operations from the users and the transmission latency of the network, some concurrent problems take place during the collaborative work. Currently, based on the researches of the real-time collaborative system, none of the existing system can solve all the concurrent problems completely. In this article, these concurrent problems are analyzed in detail, some current existing methods are discussed about their achievements and defects, then several solutions are proposed for the aim of the cosmically usage of the collaborative system.Firstly, some inconsistency problems due to the unconstraint user operations and network latency are analyzed; the causes and the results of three inconsistency problems such as divergence, causality violation and intension violation are pointed out. In this article, a series of algorithms like State Vector algorithm and undo/transformed do/transformed redo algorithm are stated out, which solve the inconsistency problems efficaciously.At the same time, some concurrent problems which are caused during the system provided undo/redo operations are discussed. As an important function in single user system, the undo/redo schema is also an indispensable system function. Due to the particularity of the undo/redo operations, to undo an operation in the collaborative system can cause the system to be inconsistent. After some researches on this problem, we propose the undo/transformed do/transformed redo algorithm in this article, which are good ways to solve the problem.During the cause of the collaborative design, if a site joins the system late, or a site disconnect from the system abnormally and rejoins in, concurrent problems will also occur, because the initial state of the design document is different. For this situation, we propose the synchronizing process algorithm,which includes steps of charging site sends the synchronizing queue, state vectors query around, renew the miss operations. This algorithm ensures the newly joined site maintains the same document state with other sites.In this article, an integrated prototype of real-time collaborative system, CoDesign system, is proposed. As a prototype of real-time collaborative system, the CoDesign system implements all the algorithms proposed in this article. This prototype is tested under the simulation of various situations happen in the cosmically usage of the collaborative system. The researches and experiments based on this prototype have proved the correctness and validity of the solutions in this article.