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. This approximation is tight in practice for automata obtained from XPath expressions, and even exact for many of them. 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.

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. This approximation is tight in practice for automata obtained from XPath expressions, and even exact for many of them. 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.

Abstract. We consider semistructured data as rooted edge-labeled directed graphs, and path inclusion constraints on these graphs. In this paper, we show that we can extract from a finite datum D a finite set C f (D) of word inclusions, which implies exactly every word inclusion satisfied by D. Then, we give a new decision algorithm for the implication problem of a constraint p q by a set of constraints pi ui where p, q, and the pi's are regular path expressions and the ui's are non empty paths, improving in this particular case, the more general algorithms of S. Abiteboul and V. Vianu, and Alechina et al. Moreover, in the case of a set of word equalities ui ≡ vi, we give a more efficient decision algorithm for the implication of a word equality u ≡ v, improving the more general algorithm of P. Buneman et al., and we prove that, in this case, the implication problem for non deterministic models or for (complete) deterministic models are equivalent.