Most of the relational database management systems (RDBMS) used nowadays provide some limited security mechanisms, and facilities offer capabilities to define roles and establish audit trails. Users of RDBMSs are used to working with discretionary access control (DAC) policies. This kind of security is sufficient for a great majority of information systems, however an increasing number of organisations are requiring a securer control mechanism such as the mandatory access control (MAC) implemented in some DBMS products. We give an overview of the MAC database models proposed both in relational and in other kinds of DBMSs (e.g. object-oriented). We review the most common architectures followed in the construction of secure DBMSs and the methodologies that are being developed for designing this kind of database.