Two-variable logic on data trees and XML reasoning

Abstract

Motivated by reasoning tasks for XML languages, the satisfiability problem of logics ondata treesis investigated. The nodes of a data tree have alabelfrom a finite set and adata valuefrom a possibly infinite set. It is shown that satisfiability for two-variable first-order logic is decidable if the tree structure can be accessed only through thechildand thenext siblingpredicates and the access to data values is restricted to equality tests. From this main result, decidability of satisfiability and containment for a data-aware fragment of XPath and of the implication problem for unary key and inclusion constraints is concluded.