We describe and implement a policy language. In our system, agents can
distribute data along with usage policies in a decentralized architecture. Our
language supports the specification of conditions and obligations, and also the
possibility to refine policies. In our framework, the compliance with usage
policies is not actively enforced. However, agents are accountable for their
actions, and may be audited by an authority requiring justifications.Comment: To appear in Proceedings of IEEE Policy 200