考虑工程图形协同应用特点的并发控制研究

并发控制是CSCW系统的关键技术，没有统一标准，通常要根据协同应用的特点来构造。文中以CAD系统内部数据库拓扑结构的一致性作为显示一致性的基础，适时放宽整体一致性模型中的事件定义条件和一致性判定条件，提出一种改进的整体一致性模型。按照该模型的事件关系定义，通过图形对象全局ID标识的一致性维护和添加操作的相关性分析，提出一种添加操作优先的并发控制策略。基于上述模型和策略，研究了一种偏复制式混合体系结构下的悲观和有限乐观的并发控制方法，以及相应的并发控制协议实施技术。工程实践证明，这些并发控制模型、策略、方法和技术充分考虑了工程图形数据结构及其协同应用特点，从而有效地支持设计过程中的人人交互。

Concurrency Control and Consistency Maintenance: A Case Study in Collaborative Engineering Graphics Design System

Concurrency control is one of the key issues in computer supported cooperative work system. However, the existing concurrency control methods widely accepted in cooperative editing, conference system and application sharing can not be applied to collaborative CAD system directly. In order to guarantee the topological structure consistency of CAD internal database as the base of display consistency, a new consistency model is presented by revising the definition and identification conditions in strict consistency model. A concurrency control strategy giving the priority to insertion operation is outlined according to the relationship between insertion operation and object ID sequence. Based on the above model and strategy, both the pessimistic and optimistic concurrency control approaches are studied. The implementation techniques and algorithms of concurrency control protocol are described. The proposed method has been implemented and tested in a CSCW tool for CAD system--CoCADToolAgent. The results demonstrate that our ideas are correct and effective to support the human-human interaction in typical design processes.