The XPath satisfiability problem is to decide, for an XPath expression q and a DTD D, if there exists an XML document t valid against D such that the answer of q on t is nonempty. It is shown that the satisfiability problem is intractable for many XPath fragments. In this paper, we focus on fixed DTDs and consider the problem under fixed DTDs. We first show that, for a very restricted XPath fra...

In this paper, we consider the XPath satisfiability problem under restricted DTDs called “duplicate free”. For an XPath expression q and a DTD D, q is satisfiable under D if there exists an XML document t such that t is valid against D and that the answer of q on t is nonempty. Evaluating an unsatisfiable XPath expression is meaningless, since such an expression can always be replaced by an emp...

XPath is the standard language for addressing parts of an XML document. We present a sound and complete decision procedure for containment of XPath queries. The considered XPath fragment covers most of the language features used in practice. Specifically, we show how XPath queries can be translated into equivalent formulas in monadic second-order logic. Using this translation, we construct an o...

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 containment is with respect to trees satisfying a set of constraints (such as a schema or DTD), the proble...

Since navigational aspects of XPath correspond to first-order definability, it has been proposed to use the analogy with the very successful technique of translating LTL into automata, and produce efficient translations of XPath queries into automata on unranked trees. These translations can then be used for a variety of reasoning tasks such as XPath consistency, or optimization, under XML sche...

Although many algorithms have been proposed for evaluating XPath queries containing child and descendant axes and predicates (XPATH/,//,[ ]) against XML data, there are very few efforts towards developing algorithms for processing path expressions with other axes namely, following, preceding, following-sibling and preceding-sibling. In this article, we demonstrate that the conventional twig-str...

Recent studies have proposed structural summary techniques for pathquery evaluation on semi-structured data sources. One major line of this research has been the introduction of the DataGuide, 1-index, 2-index, and A(k) indices, and subsequent investigations and generalizations. Another recent study has considered structural characterizations of fragments of XPath, the standard path navigation ...