The principal function of any access control system is to prohibit unauthorized individuals from entering controlled areas while allowing authorized persons access. Recognizing the person as authorized requires a method of identifying the individual. Several topics are important to access control: encoding and decoding; facilities and zones; antipassback; global antipassback; antitailgating; and intrinsic safety. Any new computerized access control systems should use a data base management system (DBMS) that allows security data and other important data to be integrated and maintained in a centralized computer, ready to be accessed by several users. Important criteria for the DBMS functions include security, data model, employee data, and data integrity. One of the major advantages of a computerized access control system is its ability to support an organization's overall operation. Considerations for an effective access control system include reliability and health monitoring, management information, data security, operations, maintenance, and performance.