A concurrency control mechanism for a networked virtual environment is a key element in many collaborative computer-aided design applications. However, conventional object-based locking mechanisms restrict the behaviors of nonowners, and an attribute-based locking mechanism may produce another problem called task-surprise, which disturbs users' collaboration. In this paper, we propose a hybrid concurrency control mechanism that reduces restrictions of nonowners' behaviors and task-surprises in a networked virtual environment. The proposed method consists of two concurrency control approaches: task-based concurrency control and personal workspaces. The task-based concurrency control approach allows nonowners to do some tasks if they do not conflict with the tasks of the owner of the shared object. The personal workspaces approach provides an independent workspace where a user can manipulate copies of the shared objects. The proposed method was applied to a collaborative level design for a large-scale online game as a case study. We evaluated its performance by experiments and user studies to check acceptance and usability of the proposed method.

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