Role-Based Access Control (RBAC) has become the de facto standard for realizing authorization requirements in a wide range of organizations. Existing RBAC models suffer from two main shortcomings; lack of expressiveness of roles/permissions and ambiguities of their hierarchies. Roles/permissions expressiveness is limited since roles do not have the ability to express behaviour and state, while hierarchical RBAC cannot reflect real organizational hierarchies. In this paper, we propose a novel access control model: The Role-Oriented Access Control Model (ROAC), which is based on the concepts of RBAC but inspired by the object-oriented paradigm. ROAC greatly enhances expressiveness of roles and permissions by introducing parameters and methods as members. The hierarchical ROAC model supports selective inheritance of permissions.