lipton studied and created database security models on how and when to restrict the queries made by users of a database such that private or secret information will not be leaked. even when the user is restricted to only read operations on a database, secure information could be at risk. for example, querying a database of campaign donations could allow the user to discover the individual donations to political candidates or organizations. if given access to averages of data and unrestricted query access, a user could exploit the properties of those averages to gain illicit information. these queries are considered to have large "overlap" creating the insecurity. by bounding the "overlap" and number of queries, a secure database can be achieved.