We describe a policy language and implement its associated proof checking system. 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.

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Privacy is a prime concern in today's information society. To protect the privacy of individuals, enterprises must follow certain privacy practices while collecting or processing personal data. In this chapter we look at the setting where an enterprise collects private data on its website, processes it inside the enterprise and shares it with partner enterprises. In particular, we analyse three different privacy systems that can be used in the different stages of this lifecycle. One of them is the audit logic, recently introduced, which can be used to keep data private while travelling across enterprise boundaries. We conclude with an analysis of the features and shortcomings of these systems.