An old problem in privacy research is understanding how publication of an anonymized relation can lead to privacy loss via background or auxiliary information. This talk examines that problem from the perspective of Dowker's duality theorem for relations. The relation itself defines two simplicial complexes: a space of attributes and a space of individuals. Dowker's theorem says that these two spaces are homotopy equivalent. That equivalence suggests two definitions of privacy: attribute-privacy and association- privacy. The talk discusses that construction and surveys some consequent results.