In the field of access control, many security breaches occur because of a lack of early means to evaluate if access control policies are adequate to satisfy privileges requested by subjects which try to perform actions on objects. This paper proposes an approach based on UMLsec, to tackle this problem. We propose to extend UMLsec, and to add OrBAC elements. In particular, we add the notions of context, inheritance and separation. We also propose a methodology for modeling a security policy and assessing the security policy modeled, based on the use of MotOrBAC. This assessment is proposed in order to guarantee security policies are well-formed, to analyse potential conflicts, and to simulate a real situation. © 2013 IEEE.