A set approach to role modeling

Most existing role modeling techniques use graphic notations for role description. There are a number of shortcomings with the graphic notations. First, they are ambiguous. Second they cannot effectively represent dynamic aspects of roles. The paper reports our initial effort on a formal notation for role description and modeling. The notation is based on the set operations. By using the set approach, role binding or unbinding to or from an object can be specified unambiguously by set union and set difference. We can also specify role constraints so that roles can be bound or unbound sequentially, alternatively, repeatedly, or simultaneously. Similarly, roles of roles can be specified by set inclusion in relation to a new context. Role specialisation or generalisation can be described by set intersection of roles. Role compositions can be specified as set unions of part roles. In addition to the set notation, we have also adapted the formal method EMS to support static and dynamic description of roles. First, all class/role relationships are captured step by step. Second, all class/role structures are described by an Object-Z-like notation, class by class and role by role. Third, all system obligations are specified using Petri net transitions, where pre and post conditions of transactions are expressed formally. Lastly, services and communications required for the objects/role instances involved in the system operations are described.