Relative compromise of statistical databases

Statistical databases are databases in which only statistical type of queries are allowed. The results of the statistical queries are intended for statistical use only. However, it has been shown that using only statistical queries it is often possible to infer an individuals's value of a protected field (e.g, using various types of trackers). In such a case we say that the database has been (positively) compromised. Various types of compromise have been studied but until now attention has centred on the inference of exact information from permitted queries. In this paper we introduce a new type of compromise, the 'relative' compromise: a set of records is relatively compromised with respect to a field X if the relative order of magnitude of the X-values of the set is known. This paper shows that even when exact information is protected, relative information may be accessible. We consider several sets of conditions under which this compromise can occur using SUM type of queries of fixed query set size, as well as some of the possible consequences of relative compromise.