Saturation, Definability, and Separation for XPath on Data Trees.
Sergio Abriola, María Emilia Descotte, Santiago Figueira · AMW · 2015
We study the expressive power of some fragments of XPath equipped with (in)equality tests over data trees. Our main results are the definability theorems, which give necessary and sufficient conditions under which a class of data trees can be defined by a node expression or set of node expressions, and our separation theorems, which give sufficient conditions under which two disjoint classes of data trees can be separated by a class of data trees definable in XPath.