Data mining is the process of extracting useful, interesting, and previously unknown information from large data sets. The success of data mining relies on the availability of high quality data and eﬀective information sharing. The collection of digital information by governments, corporations, and individuals has created an environment that facilitates large-scale data mining and data analysis. Moreover, driven by mutual beneﬁts, or by regulations that require certain data to be published, there is a demand for sharing data among various parties. For example, licensed hospitals in California are required to submit speciﬁc demographic data on every patient discharged from their facility . In June 2004, the Information Technology Advisory Committee released a report entitled Revolutionizing Health Care Through Information Technology . One key point was to establish a nationwide system of electronic medical records that encourages sharing of medical knowledge through computer-assisted clinical decision support. Data publishing is equally ubiquitous in other domains. For example, Netﬂix, a popular online movie rental service, recently published a data set containing movie ratings of 500,000 subscribers, in a drive to improve the accuracy of movie recommendations based on personal preferences (New York Times, Oct. 2, 2006); AOL published a release of query logs but quickly removed it due to the re-identiﬁcation of a searcher .