variety of XPath fragments widely used in practice, and investigate the impact of different XPath operators on satisfiability analysis. We first study the problem for negation-free XPath fragments with and without upward axes, recursion and data-value joins, identifying which factors lead to tractability

for this problem with polynomial-time combined query evaluation complexity. Moreover, we present two fragments of XPath for which linear-time query processing algorithms exist. 1

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fragment of the XPath query language, with applications in all these contexts. In particular, we study a class of XPath queries that contain branching, label wildcards and can express descendant relationships between nodes. Prior work has shown that languages that combine any two of these three features

We study structural properties of each of the main sublanguages of XPath [8] commonly used in practice. First, we characterize the expressive power of these language fragments in terms of both logics and tree patterns. Second, we investigate closure properties, focusing on the ability to perform

This survey gives an overview of formal results on the XML query language XPath. We identify several important fragments of XPath, focusing on subsets of XPath 1.0. We then give results on the expressiveness of XPath and its fragments compared to other formalisms for querying trees, algorithms

The containment and equivalence problems for various fragments of XPath have been studied by a number of authors. For some fragments, deciding containment (and even minimisation) has been shown to be in ptime, while for minor extensions containment has been shown to be conp-complete. When

formulated with the help of XPath expressions. Our core formalism consists of a fragment of XPath that we call simple and a corresponding class of of integrity constraints that we call simple XPath integrity constraints (SXIC). SXIC's can express many database-style constraints, including key

large and practically important fragment of XPath 1.0 for which the combined complexity is LOGCFL-complete and, therefore, in the highly parallelizable complexity class NC2.

We present a query answering algorithm for a fragment of Forward XPath on Xml streams that we obtain by compilation to deterministic nested word automata. Our algorithm is earliest and in polynomial time. This proves the finite streamability of the fragment of Forward XPath with child steps