XPath containment in the presence of disjunction, DTDs, and variables.

Abstract

XPath is a simple language for navigating an XML tree and returning a set of answer nodes. The focus in this paper is on the complexity of the containment problem for various fragments of XPath. In addition to the basic operations (child, descendant, filter, and wildcard), we consider disjunction, DTDs and variables. W.r.t. variables we study two semantics: (1) the value of variables is given by an outer context; (2) the value of variables is defined existentially.We establish an almost complete classification of the complexity of the containment problem w.r.t. these fragments.