Structural characterizations of the semantics of XPath as navigation tool on a document

Given a document D in the form of an unordered labeled tree, we study the expressibility on D of various fragments of XPath, the core navigational language on XML documents. We give characterizations, in terms of the structure of D, for when a binary relation on its nodes is definable by an XPath expression in these fragments. Since each pair of nodes in such a relation represents a unique path in D, our results therefore capture the sets of paths in D definable in XPath. We refer to this perspective on the semantics of XPath as the "global view." In contrast with this global view, there is also a "local view" where one is interested in the nodes to which one can navigate starting from a particular node in the document. In this view, we characterize when a set of nodes in D can be defined as the result of applying an XPath expression to a given node of D. All these definability results, both in the global and the local view, are obtained by using a robust two-step ...

• Type: Conference
• Year: 2006
• Where: PODS
• Authors: Marc Gyssens, Jan Paredaens, Dirk Van Gucht, George H. L. Fletcher
• Keywords: Database, Global View, Keywords XPath, PODS 2006, XPath Expression