A permission is a named value conferring the ability (or formal
consent) to perform actions in a system. We focus mainly on
permissions based on Access control policies, that grant permissions
to principals on the basis of security attributes or privileges
typically maintained via Access Control Lists (ACLs). In order to
make an control decision, access decision functions compare the
permissions granted to a principal against the permissions required to
perform an operation. For example, permission to read a file
/tmp/foo.txt can be denoted as
FilePermission: read:/tmp/foo.txt.