A Unified Model for Security and Integrity in Relational Databases

T h e issues of database security and integrity are tightly related. Security mechanisms and integrity mechanisms are both concerned with protection of information, and both involve management of meta-information and procedures for screening transactions. Yet in database systems these tasks are entirely separate. In this paper we describe a unified model that accommodates both security and integrity, with all protective restrictions stated in terms of database views. These protective restrictions are treated as knowledge, from which transaction screening procedures infer the restrictions tha t apply to individual transactions. A transaction may be allowed or denied in its entirety, or specific non-violating subtransactions may be identified. This process is an application of the view inference problem, to which we offer two alternative solutions. We then show how users can exploit information made available by the integrity mechanism to bypass the security mechanism, and discuss how such security breaches can be avoided. Finally, we show how the model can accommodate a broader concept of integrity that was introduced recently.