Efficient comparison of enterprise privacy policies

Enterprise privacy policies often reflect different legal regulations, promises made to customers, as well as more restrictive enterprise-internal practices. The notion of policy refinement is fundamental for privacy policies, as it allows one to check whether a company's policy fulfills regulations or adheres to standards set by customer organizations, to realize the "sticky policy paradigm" that addresses transferring data from one realm to another in a privacy-preserving way, and much more. Although well-established in theory, the problem of how to efficiently check whether one policy refines another has been left open in the privacy policy literature. We present a practical algorithm for this task, concentrating on those aspects that make refinement of privacy policies more difficult than, for example refinement for access control policies, such as a more sophisticated treatment of deny rules and a suitable way for dealing with obligations and conditions on context information.