Polynomial time fragments of XPath with variables
Emmanuel Filiot, Joachim Niehren, Jean-Marc Talbot, Sophie Tison · 2007
Variables are the distinguishing new feature of XPath 2.0 which permits to select n-tuples of nodes in trees. It is known that the Core of XPath 2.0 captures n-ary first-order (FO) queries modulo linear time transformations. In this paper, we distinguish a fragment of Core XPath 2.0 that remains FO-complete with respect ton-ary queries while enjoying polynomial-time query answering.