We consider a fragment of XPath named ‘forward-XPath’, which contains all descendant and rightwards sibling axes as well as data equality and inequality tests. The satisfiability problem for forward-XPath in the presence of DTDs and even of primary key constraints is shown here to be decidable. To show decidability we introduce a model of alternating automata on data trees that can move downwar...

In this paper we present an extension of the XPath query language for the handling of flexible queries. In order to provide ranked answers, our approach proposes fuzzy variants of and, or and avg operators for XPath conditions, as well as two structural constraints, called down and deep, for which a certain degree of relevance is associated. Our proposal has been implemented with a fuzzy logic ...

XPath is simple query language for XML documents which allows navigating in XML trees and returning a set of matching nodes. It is used in XML Schema to define keys and in XLink and XPointer to reference portions of documents. XPath is a fundamental part of the XSLT and XQuery languages as it allows definition of matching expressions for patterns and provides node selectors to filter elements i...

We study the expressive power of some fragments of XPath equipped with (in)equality tests over data trees. Our main results are the definability theorems, which give necessary and sufficient conditions under which a class of data trees can be defined by a node expression or set of node expressions, and our separation theorems, which give sufficient conditions under which two disjoint classes of...

The key function parts of an XML query system include XML parsing, XPath and XQuery evaluation. Each part has its specific parallel opportunity and approach. And the efficiency of each part directly affects the overall effect of XML query parallelization. Therefore it is necessary to coordinate each part in a real query application to achieve the best overall parallel performance. In this paper...

An XML publish/subscribe system needs to match many XPath queries (subscriptions) over published XML documents. The performance and scalability of the matching algorithm is essential for the system when the number of XPath subscriptions is large. Earlier solutions to this problem usually built large finite state automata for all the XPath subscriptions in memory. The scalability of this approac...

We give sound and complete axiomatizations for XPath with data tests by ‘equality’ or ‘inequality’, and containing the single ‘child’ axis. This data-aware logic predicts over data trees, which are tree-like structures whose every node contains a label from a finite alphabet and a data value from an infinite domain. The language allows us to compare data values of two nodes but cannot access th...

We propose a new approach for the efficient evaluation of XPath expressions. This is important, sinceXPath is not only used as a simple, stand-alone query language, but is also an essential ingredient ofXQuery and XSLT.The main idea of our approach is to translate XPath into algebraic expressions parameterized withprograms. These programs are mainly built from navigational p...

XML and the XPath querying language have become ubiquitous data and querying standards used in many industrial settings and across the World-Wide Web. The high latency of XPath queries over large XML databases remains a problem for many applications. While this latency could be reduced by parallel execution, issues such as work partitioning, memory contention, and load imbalance may diminish th...