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Whereas access control describes the conditions that have to be fulfilled before data is released, usage control describes how the data has to be treated after it is released. Usage control can be applied to digital rights management, where the data are usually copyright-protected media, as well as in privacy, in which case the data are privacy-sensitive personal information. An important aspect of usage control for privacy, especially in light of the current trend towards composed web services (so-called mash-ups), is downstream usage, i.e., with whom and under which usage control restrictions data can be shared. In this work, we present a two-sided XML-based policy language: on the one hand, it allows users to express in their preferences in a fine-grained way the exact paths that their data is allowed to follow, and the usage restrictions that apply at each hop in the path. On the other hand, it allows data consumers to express in their policies how they intend to treat the data, with whom they intend to share it, and how the downstream consumers intend to treat the data.