Collaborative Graphics Editing Systems

Cooperative Graphics Editing System (CGES) is a very hot research area in these days. But in the research and development of many such systems, such as: CaveDraw, VideoDra, and the Shared Whiteboard integrated in the MILAN system, there are several fairly common problems, e.g. the system architecture lacks enough extensibility and adaptability, the data sharing region and model supported in these systems is too simple, most of the concurrency control schemes applied in these systems bring about too many abundant operations, most of the systems lack the systematic support for conflicts detection and resolution, and there are too little suitable toolkits to support their development.To resolve the above problems, new methods and techniques have to be introduced, which has made up the main parts of this thesis. The main contribution of this paper is described as the following:1. Based on the analyze of the existing system architectures utilized in CSCW applications, and to satisfy the requirements of the cooperative editing work, I introduced the so called tree based distributed architecture. The new architecture could be easily expanded and freely configured, and also with the load of each site in the system balanced.2. Based on the new system architecture, personal data and shared data could be easily distinguished and many different data sharing modes could be created by applying the concept of data sharing region and the corresponding maintenance techniques.3. It is a basic requirement for the CGES to give participants the feeling of consistency to the shared objects. In this paper, I introduced a local consistency model as a simplification to the global consistency model utilized in many current CGES. The concurrency control scheme based on this model is also presented. According to this scheme, only when the target of an operation falls into the overlapped display regions of other users, it is then transferred and executed remotely. Consequently, the abundant operations are removed and the network load and the time for concurrency control are greatly reduced.4. Based on the current researches on the occurrence and...