Research And Implementation Of The Key Technologies In Distributed Cooperative Graphics Editing System

Cooperative Graphics Editing System (CGES) is an important branch in Collaborative Editing System research field. To support multi-user cooperative editing synchronously, CGES should have the characteristics of real-time response, transparent and unconstraint cooperation-support. Generally, in order to achieve this, we adopt Distributed Architecture as its editing mode, which means that shared-graphics-document is replicated to each local client so that all operations (such as refreshing, updating, deleting and creating) on it can be performed at local site immediately. Consequently, how to guarantee the view consistency and initial-state-synchronization for each distributed collaborative user in Distributed Architecture is the key issue of CGES, which is also the core of this paper.This paper is focused on above two key techniques in CGES, and we propose two algorithms as their resolutions and apply them to the project of "Digital-meeting-oriented Wireless Projector Information Sharing Platform" successfully:Firstly, for the view consistency problem, we study the causes and representations of causality conflict and intention conflict, and propose a concurrency control algorithm bpOPT based on CGES's consistency model. bpOPT is featured with object-characteristic-based and operation-relation-based in Distribute Architecture, and it can handle conflicts effectively to achieve the consistency. Moreover, bpOPT eliminates redundant operation information and optimizes performance of concurrency control.Secondly, aimed at the un-synchronous initialization problem caused by latecomer, we put forward an improved single "Late Join Server" algorithm isLJS, which ensures the integrality and reliability of synchronous information for single latecomer or multi-latecomers to join an ongoing session. In addition, isLJS has a reliable fault-tolerant mechanism to ensure the system running normally.At the end of this paper, a prototype, Wi.jector system, is introduced based on the above algorithms. We experiment it in wireless LAN environment and simulate various inconsistent and un-synchronous situations. The experiment results indicate that the algorithms proposed in this paper are verified.