基于ＳＱＬ的ＸＭＬ查询的有效实现

讨论了关系数据库中利用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的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了方法是有效的。

EFFECTIVE EVALUATION OF XML QUERIES WITH SQL STATEMENTS

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.