中文摘要：

如何刻画知识库不同版本之间的区别是研究知识库动态更新中的一个重要问题。提出了命题逻辑知识库的逻辑结论差概念（称为逻辑差）。然而，一般知识库之间逻辑差的计算是不易处理的，而且不满足范畴性，即不能保证其结果仍然可以用同类型的知识库来表达；由于2-CNF理论的可满足问题的易处理性，证明了2-CNF理论的逻辑差具有范畴性，并设计了一个多项式时间算法计算它们的逻辑差。

英文摘要：

It is important to capture the difference between different versions of a knowledge base, in the view of dynamical change. First of all, this paper introduced the notion of logical difference for propositional knowledge bases. However, computing the difference was generally intractable. The logical difference of a class of knowledge base was possibly not categorical,i, e. , the difference couldn＇ t be presented in the same domain. Due to the tractability for the satisfiability of 2-CNF theories, it was proved that the logical difference of 2-CNF theories was categorical, and developed a polynomial-time algorithm to compute the logical difference between two 2-CNF theories.