Early Nested Word Automata for XPath Query Answering on XML Streams

Algorithms for answering XPath queries on Xml streams have been studied intensively in the last decade. Nevertheless, there still exists no solution with high efficiency and large coverage. In this paper, we introduce early nested word automata in order to approximate earliest query answering algorithms for nested word automata in a highly efficient manner. We show that this approximation can be made tight in practice for automata obtained from XPath expressions. We have implemented an XPath streaming algorithm based on early nested word automata in the Fxp tool. Fxp outperforms most previous tools in efficiency, while covering more queries of the XPathMark benchmark.