Due to the correspondence between the role abstraction in Role-based Access Control (RBAC) and the notion of organizational positions, it seems easy to construct role hierarchies. This is, however, a misconception. This paper argues that, in order to reflect the functional requirements, a role hierarchy becomes very complex. In a bid to simplify the design of role hierarchies suitable for the expression of access control requirements in workflow systems, the paper proposes a ``typed'' role hierarchy. In a ``typed'' role hierarchy a role is of a specific type. The associations between different types of roles are limited by rules that govern the construction of a role hierarchy. This paper proposes a methodology to systematically construct a ``typed'' role hierarchy. Since the ``typed'' nature of the role hierarchy is only relevant during the construction of the role hierarchy, it can seamlessly be integrated into existing RBAC schemes that support the concept of role hierarchies.