Policy Graph‌ Sample Clauses

Policy Graph‌. Policy Graph without Constraint. We first study the problem in the whole domain S without any constraint. Given the true state sx at a timestamp, a user may prefer to hide sx in a group of candidate states, denoted by N (sx) as neighbors of sx where N (sx) Ď S. Intuitively, the more neighbors a state has, the more privately it is protected. For simplicity, we assume si < N (si) for all states si because it is straightforward that si is hidden in its neighbor set N (si). We can represent the privacy policy by a undirected graph where a node represents a state and an edge connects an indistinguishable pair of states. The graph has to be undirected for the following reason. When the true state is si, we can draw edges from si to all sj < N (si). The edge sisj means si and sj are indistinguishable given true state si. On the other hand, when true state is sj, the indistinguishability sjsi also has to hold. Otherwise an adversary may infer that si and sj are only connected when si is the true state. Therefore, the edge sisj is undirected, meaning it holds for both si and sj. s1 s2 s3