A Compact and Efficient Labeling Scheme for XML Documents

Abstract

As XML data nowadays are extensively used in the applications of data exchange and other fields, supporting efficient query processing on XML data, particularly in determining the structural relationships between two elements, is in great demand recently. To avoid the time-consuming tree traversal tasks, many labeling schemes have been proposed to assign each node a unique label, so that the structural relationships between nodes, such as the ancestor-descendant relationship, can be efficiently determined by comparing their labels. However, to the best of our knowledge, none of the existing labeling schemes can support all structural relationships in constant time and also require the least amount of space. In this paper, we propose a labeling scheme based on the concept of the complete tree, which is called the CT (complete-tree) labeling scheme. This labeling scheme is simple and the resultant labels are compact. We formally analyze its properties and perform an empirical evaluation between the CT labeling scheme and other state-of-the-art labeling schemes on different data sets. The experimental results show that the space requirement of our CT labeling scheme is superior to others in most cases. It is also demonstrated that this scheme can efficiently support all structural relationships and may perform even better than other labeling schemes.