Access control is the selective restriction of access to some kind of resource (a folder, a file, and a device). There are different types of approaches to access control. The first one is Discretionary Access Control (DAC) in which every user can decide who can, with which permissions, read his/her files.

An example of this is the Unix permission system where, if you create a file, you can choose who will be able to read or change it.

In Mandatory Access Control (MAC), the administrator decides the security policies and all the files in the system will comply.

An example of this is a public archive (that is, tax archive), where even if you are the creator of a document, you are not allowed to choose who is able to read it. Only the archive owner will be able to make such decisions.

An evolution of DAC and MAC is Role-based Access Control (RBAC). In RBAC, the permissions are not granted per user, but according to role. This allows big organizations to assign permission to roles and roles to users, making it easier to create, modify, or delete users.

Examples of this type of access controllers are pretty common in day-to-day life. A typical use of RBAC in real life is the authorized personnel only area, where usually all people with certain characteristics (that is, be it an employee of a specific company or be it the work for a specific department) are allowed to enter.

An evolution of RB and MAC is Multi Level Security (MLS). In MLS systems, each user has a trust level and each item has a confidentiality level. The administrator is still the one who is in charge of creating the security policies, as in MAC systems, but the system will ensure that each user will only see the items that have a confidentiality level allowed to him based on some system configurations and the user trust level.