p121-xu - Rewriting XPath Queries Using Materialized Views...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Rewriting XPath Queries Using Materialized Views Wanhong Xu Z. Meral Ozsoyoglu Center for Computational Genomics Department of Electrical Engineering and Computer Science Case Western Reserve University, Cleveland, OH { wanhong, meral } @case.edu Abstract As a simple XML query language but with enough expressive power, XPath has become very popular. To expedite evaluation of XPath queries, we consider the problem of rewriting XPath queries using materialized XPath views. This problem is very important and arises not only from query optimization in server side but also from semantic caching in client side. We consider the problem of decid- ing whether there exists a rewriting of a query using XPath views and the problem of finding minimal rewritings. We first consider those two problems for a very practical XPath frag- ment containing the descendent, child, wild- card and branch features. We show that the rewriting existence problem is coNP-hard and the problem of finding minimal rewritings is p 3 . We also consider those two rewriting problems for three subclasses of this XPath fragment, each of which contains child feature and two of descendent, wildcard and branch features, and show that both rewriting prob- lems can be polynomially solved. Finally, we give an algorithm for finding minimal rewrit- ings, which is sound for the XPath fragment, but is also complete and runs in polynomial time for its three subclasses. 1 Introduction Recently, more and more data are represented and ex- changed as XML documents over Internet. XPath Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the VLDB copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Very Large Data Base Endowment. To copy otherwise, or to republish, requires a fee and/or special permission from the Endowment. Proceedings of the 31st VLDB Conference, Trondheim, Norway, 2005 [11], recommended by W3C, is a simple but pop- ular language to navigate XML documents and ex- tract information from them. XPath is also used as sub-languages of other XML query languages such as XQuery [5] and XSLT [12]. Since this language is popular, there has been a lot of work done to speedup evaluation of XPath queries, for example: index techniques [10, 29], structural join algorithms [1, 6] and minimization of XPath queries [2, 30, 28, 15]. More recently, the problem of rewriting queries using materialized XML views has begun to attract more attention. This rewriting problem has been first discussed for semantic caching because semantic caching can im- prove performance significantly in traditional client- server databases and Web-based information systems....
View Full Document

This note was uploaded on 03/01/2010 for the course ICT ... taught by Professor ... during the Three '10 term at University of Sydney.

Page1 / 12

p121-xu - Rewriting XPath Queries Using Materialized Views...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online