Order-Aware Twigs: Adding Order Semantics to Twigs

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-structure, which is used to represent expressions in the subset XPATH/,//,[ ], has no order information built into it and hence fails to model XPath expressions with ordered axes. This motivates us to introduce a new type of twig-structure, which we call Order-aware Twig, to effectively represent XPath expressions with ordered axes.