In this paper, a problem is studied, which evaluates XML queries using SQL statements in relational database systems. At first, an algorithm is proposed, which rewrites a regular path expression based XML query as a group of simple path expression based queries using mapping information(mapping graph). A key problem in this process is that a Kleene expression cannot be rewritten using mapping graph directly. To handle this problem, statistical information of path instances is gathered to expand Kleene expressions. After that, an approach to rewrite a simple path expression into a SQL statement is described. The approaches presented are implemented in a virtual XML-relational prototype system VXMLR. A preliminary performance study shows that the approaches are very effective.%讨论在关系数据库中利用SQL语句实现XML查询的问题.首先提出了一个利用映射信息(映射图)将带正则路径表达式的XML查询重写为一组简单路径查询的算法.该过程中的一个关键问题是Kleene表达式不能直接利用映射图重写，为此，提出了利用路径实例的统计信息来扩展Kleene表达式的算法.然后，进一步描述了将简单路径表达式查询重写为SQL查询的方法.这些算法在XML-关系系统原型VXMLR中实现.初步性能研究表明提出的方法是有效的.
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