125 Copyright © 2010, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. Chapter 6 Labeling XML Documents Jiaheng Lu School of Information and DEKE, MOE, Renmin University of China Liang Xu School of Computing, National University of Singapore Tok Wang Ling School of Computing, National University of Singapore Changqing Li Duke University, USA INTRODUCTION XML has become a de facto standard for data exchange and representation on the World Wide Web and elsewhere. To facilitate query process- ing over XML data that conforms to an ordered tree-structured data model, two main techniques have been proposed including structural index and labeling approach. Compared with the traditional methods that performs hierarchical traversal of the XML tree, the labeling approach benefits from smaller storage size and efficient establishment of various relationships such as Ancestor-Descendant (AD) and Parent-Child (PC). As a result, we con- sider labeling as the preferred approach for XML query processing. We classify existing labeling schemes into two main bodies: static labeling schemes and dynamic labeling schemes which are designed for static and AbsTRACT XML labeling schemes play an important role in XML query processing. Containment and Preix labeling schemes are two of the most popular labeling schemes. In order to perform eficient XML query process- ing, this chapter shows how to extend the traditional preix labeling scheme to speedup query processing. In addition, for XML documents that are updated frequently, many labeling schemes require relabeling which can be very expensive. A lot of research interest has been generated on designing dynamic XML labeling schemes. Making labeling schemes dynamic turns out to be a challenging problem and many of the approaches proposed only partially avoid relabeling. This chapter describes some recently emerged dynamic labeling schemes that can completely avoid relabeling, making eficient update processing in XML database management systems possible. DOI: 10.4018/978-1-61520-727-5.ch006