Abstract

Abstract XML has emerged as a semantic markup language for documents as well as the de facto language for data exchange over the World Wide Web. Declarative query languages, such as XPath and XQuery, are proposed for querying over large volumes of XML data. A number of techniques have been proposed to evaluate XML queries more efficiently. Many of these techniques assume a tree model of XML documents and are, therefore, also applicable to other data sources that can be explicitly or implicitly translated into a similar data model. The focus of this thesis is on efficient evaluation and optimization of path expressions in native XML databases. Specifically, the following issues are considered: storage system design, design of physical operators and efficient execution algorithms, and the cost-based query optimizer. The proposed storage system linearizes the tree structure into strings that can be decomposed into disk pages. Simple statistics are kept in the page headers to facilitate I/O-efficient navigation. Based on this storage system, a hybrid approach is developed to evaluate path expressions that exploit the advantages of navigational and join-based

Citations