Abstract
Work flows model and control the execution of business process in an organization. They are typically comprised of tasks or logical steps in the business process. To mitigate the ability of insiders to commit fraud, care should be taken that people authorized to perform critical tasks cannot collude. This is typically done through the specification of separation of duty (SOD)constraints. SOD constraints impose restrictions on which users or roles can be assigned to tasks and have been discussed widely in the research literature in the context of a single work flow instance. In this paper, we argue that SOD constraints that span multiple instances of a work flow also need to be considered to mitigate the security fraud. To this end, we extend the notion of SOD to include constraints that span multiple executing instances of a work flow and constraints that also take into consideration the history of completed work flow instances. We present a constraint specification language to specify the inter-instance constraints and propose methodologies to identify the cases in which certain SOD specifications would result in an anomaly . Specifically, we identify 3 types of anomalies, namely, inconsistency, depletion anomaly and overlapping anomaly The identification and rectification of anomalies are done at both the work flow specification time as well as at runtime,as appropriate,so that users can be assigned to tasks in a consistent manner.