基于区域划分的XML结构连接

结构连接是XML查询处理的核心操作,受到了研究界的关注.高效的算法是高效查询处理的关键.目前已经提出了许多结构连接的算法,它们中的大多数都基于如下的前提条件之一:输入元素集合存在索引或者有序.当这些条件不成立时，由于对输入数据临时排序或建索引的代价，这些算法的性能会大大下降.基于这样的观察，提出了一种基于区域划分的结构连接算法.该算法基于任务分解的思想，利用区域编码的特点对输入集合进行划分.给出了详细的算法设计，并对算法的I/O复杂性进行了分析.大量的实验结果显示，该算法具有良好的 性能，在输入数据无序或没有索引的情况下优于现有的排序合并算法，可以为查询计划提供更多的选择.

Structural Join of XML Based on Range Partitioning

Structural join is the core operation in XML query processing, and catches the research community's attention. Efficient algorithm is the key of efficient query processing. There have been a number of algorithms proposed for structural join, and most of them are based on one of the following assumptions: the input element sets either have indexes or are ordered. When these assumptions are not true, the performance of these algorithms will become very bad due to the cost of sorting input sets or building index on the fly. Motivated by this observation, a structural join algorithm based on range partitioning is proposed in this paper. Based on the idea of task decomposition, this algorithm takes advantage of the region numbering scheme to partition the input sets. The procedure of the algorithm is described in detail, and its I/O complexity is analyzed. The results of the extensive experiments show that this algorithm has good performance and is superior to the existing sort-merge algorithms when the input data are not sorted or indexed. It can provide query plans with more choices.