What is graham-denning model?

The Graham-Denning model is a well-known access control model developed by Michael A. Graham and Peter D. Denning in 1972. It is a formal approach to defining and implementing access control policies in a computer system. The model uses a matrix to represent the privileges that a user has over objects.

The Graham-Denning model is relationship-oriented where each subject-object relationship gets a unique name and a list of permissions associated with it. This model provides an explicit and systematic mechanism to grant and revoke access rights by using the following operations:

1. Create a new subject

2. Delete an existing subject

3. Create a new object

4. Delete an existing object

5. Grant permission to a subject to access an object

6. Revoke permission to a subject to access an object

The Graham-Denning model is based on three main rules:

1. The create rule: A subject S can create a new subject S' if and only if S has the create access right to S' and S' does not already exist.

2. The delete rule: A subject S can delete a subject S' if and only if S has the delete access right to S' and S' does not have any active access rights.

3. The grant rule: A subject S can grant a subject S' a permission P on an object O if and only if S has the grant access right to P and S' does not already have the permission P on O.

Overall, the Graham-Denning model is considered to be a powerful and comprehensive model for access control in computer systems. It provides a formal and precise way to express and enforce access control policies for a wide range of applications.