复制式协同图形编辑环境中复合Undo操作语义一致性维护研究*

复制式架构下的二维CAD协同图形编辑环境中，用户界面所发出的Undo操作从语义上讲是针对复合操作本身的，但传统的一致性维护算法是基于原子操作的，对Undo操作的支持也是以原子操作为单位的，这样就会导致复合Undo操作的语义不一致性问题。分析了CAD图形编辑环境中复合操作的类型及Undo操作的执行前提，讨论了Undo操作存在的情况下的冲突定义，提出了基于版本分裂机制的冲突解决策略，并描述了复合Undo操作在本地和远程站点的执行流程及主要算法。最后通过实例分析证明了该方法的有效性。

Maintaining semantic consistency of compound Undo operations in replicated collaborative graphical editing environments

The Undo operations released at user interface in replicated collaborative graphical CAD two-dimensional editing environments are targeted at compound operations, but not decomposed basic ones. However, the traditional consistency maintenance algorithms are based on basic operations, so that the process of Undo operations also takes basic operation as the manipulation unit, thus leading to semantic inconsistencies of compound Undo operations. This paper analyzed the compound operations types and the Undo preconditions, discussed the conflict definition of different operations and introduced the version-decomposition strategy as the resolution method, and described the control flow and the main algorithms of the execution process of the compound Undo operations. A case analysis show the effectiveness of the strategy.