A Formal Foundation for ODRL
  ODRL is a popular XML-based language for stating the conditions under which resources can be accessed legitimately. The language is described in English and, as a result, agreements written in ODRL are open to interpretation. To address this problem, we propose a formal semantics for a representative fragment of the language. We use this semantics to determine precisely when a permission is implied by a set of ODRL statements and show that answering such questions is a decidable NP-hard problem. Finally, we define a tractable fragment of ODRL that is also fairly expressive. 
Riccardo Pucella and Vicky Weissman