OS-Access Control Matrix

One way to control access to files is to create a two-dimensional access control matrix listing all the users and all the files in the system. The entry Aij is 1 if user i is allowed access to file j

Otherwise Aij=0. In an installation with a largae number of users and a large number of files, this matrix would be very large and very sparse. Allowing one user access to another users files.



To make a matrix concept useful, it would be necessary to use codes to indicate various kinds of access such as read only, write only, execute only, read write etc.

ACCESS CONTROL BY USER CLASSES:

A technique that requires considerably less space is to control access to various user classes. A common classification scheme is
  1.  Owner – Normally, this is the user who created the file.
  2.  Specified User - The owner specifies that another individual may use the file.
  3.  Group or Project – Users are often members of a group working on a particular project. In this case the various members of the group may all be granted access to each other’s project-related files.
  4.  Public- Most systems allow a file to be designated as public so that it may be accessed by any member of the system’s user community. Public access normally allows users to read or execute a file, but not to write it.
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