On the operational semantics of rights expression languages

We propose an operational model for formalising and enforcing rights expression languages based on the concept of a rights expression compiler. Our compiler transforms an XML-based rights expression into a programme for a virtual machine. This approach provides a formal way of defining semantics for rights expression languages that can be directly used in practice to enforce the expressions while ensuring their consistency and correctness. We further argue that our model eliminates a number of limitations in previous attempts to associate rights expression languages with formal semantics. We demonstrate the power and practicality of our model by using it to develop operational semantics for the OMA Rights Expression Language, from which a real interpreter can be derived with relatively little effort.