Abstract: This paper gives a solution based on lazyDFA technology and presents the optimized algorithm which aims at the XPath query processing and query optimization problem over XML data stream.Shared NFA state table，which divides the states in NFA into two sets，they are shared set and exclusive set.By this algorithm we can reduce the memory usage of lazyDFA.Another optimizational algorithm adds a state transition table in lazyDFA structure，which can improve lazyDFA query speed.The experimental results show that the method is superior to the traditional algorithms in the implementational efficiency and spacial cost.

Key words: XML data stream, XPath, lazyDFA, query optimization

摘要： 针对XML数据流上XPath查询处理及查询优化问题，给出了一种基于lazyDFA技术的解决方案，并提出了优化算法。共享NFA状态表，通过将NFA中的状态分成共享和独享两个状态集来降低lazyDFA的内存使用量；建立状态转移表优化算法通过在lazyDFA状态结构中增加一个状态转移表，来提高lazyDFA的查询速度。实验结果表明，提出的方法能够在执行效率和空间代价方面优于传统算法。

关键词: XML数据流, XPath, lazyDFA, 查询优化