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As online social networks are becoming part of both social and work life, preserving privacy of their users is becoming tremendously difficult. While these social networks are promising privacy through privacy agreements, everyday new privacy leakages are emerging. Ideally, online social networks should be able to manage and maintain their agreements through wellfounded methods. However, the dynamic nature of the online social networks is making it difficult to keep private information contained.We have developed PROT OSS, a run time tool for detecting privacy leakages in online social networks. PROT OSS captures relations among users, their privacy agreements with an online social network operator, and domain-based inference rules. It then uses model checking to detect if an online social network will leak private information.

We propose a diagnosis procedure that agents can use to explain exceptions to contract executions. Contracts are expressed by social commitments associated with temporal constraints. The procedure reasons from the relations among such commitments, and returns one amongst different possible mismatches that may have caused an exception. In particular, we consider two possibilities: misalignment, when two agents have two different views of the same commitment, and misbehavior, when there is no misalignment, but a debtor agent fails to oblige. We also provide a realignment policy that can be applied in case of a misalignment. Our formalization uses a reactive form of Event Calculus. We illustrate the workings of our approach by discussing a delivery process from e-commerce as a case study.

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