中文摘要：

用况是捕获需求的主要工具之一．随着系统复杂性的增长，系统涉众数目急剧增加，需求捕获变得更为困难．解决系统复杂性问题的常用方法是采用分而治之的策略，从不同涉众中得到系统需求的不同方面，然后将不同方面的需求合并为完整需求模型．随之而来的问题是不同用况之间的重叠，就是相同或相似的事件流片断出现在多个用况中．重复事件流片断会降低模型的可维护性、可理解性，增加系统开发成本．虽然人们已经意识到了这个问题，但缺乏相应的检测算法．本文给出基于信息检索技术的启发式检索算法以检测相似事件流片断．实验结果表明算法是有效的．

英文摘要：

In order to deal with the complexity of large systems, the divide-and-conquer policy is adopted in requirements engineering： collect requirements from different groups of stakeholders, and then compose them together as a complete requirements specification. However, the policy brings forward the problem of overlapping use cases： similar event flows appear in more than one use case. Duplicate event flows lower the readability and maintainability of use case diagrams. The problem has been recognized, but no detecting approach is available to find out duplicate event flows. The paper proposes a heuristic algorithm which is based on information retrieval technologies. Evaluation results suggest that the algorithm is efficient and effective.