Optimizing performance of workflow executions under authorization control

“Business processes or workflows are often used to model enterprise or scientific applications. It has received considerable attention to automate workflow executions on computing resources. However, many workflow scenarios still involve human activities and consist of a mixture of human tasks and computing tasks. Human involvement introduces security and authorization concerns, requiring restrictions on who is allowed to perform which tasks at what time. Role- Based Access Control (RBAC) is a popular authorization mechanism. In RBAC, the authorization concepts such as roles and permissions are defined, and various authorization constraints are supported, including separation of duty, temporal constraints, etc. Under RBAC, users are assigned to certain roles, while the roles are associated with prescribed permissions. When we assess resource capacities, or evaluate the performance of workflow executions on supporting platforms, it is often assumed that when a task is allocated to a resource, the resource will accept the task and start the execution once a processor becomes available. However, when the authorization policies are taken into account,” this assumption may not be true and the situation becomes more complex. For example, when a task arrives, a valid and activated role has to be assigned to a task before the task can start execution. The deployed authorization constraints may delay the workflow execution due to the roles’ availability, or other restrictions on the role assignments, which will consequently have negative impact on application performance. When the authorization constraints are present to restrict the workflow executions, it entails new research issues that have not been studied yet in conventional workflow management. This thesis aims to investigate these new research issues. First, it is important to know whether a feasible authorization solution can be found to enable the executions of all tasks in a workflow, i.e., check the feasibility of the deployed authorization constraints. This thesis studies the issue of the feasibility checking and models the feasibility checking problem as a constraints satisfaction problem. Second, it is useful to know when the performance of workflow executions will not be affected by the given authorization constraints. This thesis proposes the methods to determine the time durations when the given authorization constraints do not have impact. Third, when the authorization constraints do have the performance impact, how can we quantitatively analyse and determine the impact? When there are multiple choices to assign the roles to the tasks, will different choices lead to the different performance impact? If so, can we find an optimal way to conduct the task-role assignments so that the performance impact is minimized? This thesis proposes the method to analyze the delay caused by the authorization constraints if the workflow arrives beyond the non-impact time duration calculated above. Through the analysis of the delay, we realize that the authorization method, i.e., the method to select the roles to assign to the tasks affects the length of the delay caused by the authorization constraints. Based on this finding, we propose an optimal authorization method, called the Global Authorization Aware (GAA) method. Fourth, a key reason why authorization constraints may have impact on performance is because the authorization control directs the tasks to some particular roles. Then how to determine the level of workload directed to each role given a set of authorization constraints? This thesis conducts the theoretical analysis about how the authorization constraints direct the workload to the roles, and proposes the methods to calculate the arriving rate of the requests directed to each role under the role, temporal and cardinality constraints. Finally, the amount of resources allocated to support each individual role may have impact on the execution performance of the workflows. Therefore, it is desired to develop the strategies to determine the adequate amount of resources when the authorization control is present in the system. This thesis presents the methods to allocate the appropriate quantity for resources, including both human resources and computing resources. Different features of human resources and computing resources are taken into account. For human resources, the objective is to maximize the performance subject to the budgets to hire the human resources, while for computing resources, the strategy aims to allocate adequate amount of computing resources to meet the QoS requirements

Human workflow modelling in homogeneous computor networks

Maintaining consistent operational efficiency and productivity levels through effective and reliable workflow processes can be the key to businesses realising long-term profit margins. This can be difficult to achieve if the challenges that affect this dual paradigm are not fully understood. Where human input is an integral part of the business workflow, the existing methods for modelling this human interaction are too abstract in nature and are not appropriate for deriving performance characteristics about human input into the process. This paper introduces a novel approach to classifying humans for the purpose of workflow modelling. Following this classification we further demonstrate that an analytical method, such as queueing theory, can be used to extract the resource utilisation and throughput characteristics of humans engaged in a business workflow processes. The initial results from experimentations indicate that the resource utilisation and throughput levels of humans could provide insight into where performance gains and increased throughput can be made. We do not consider the unique behavioural characteristics of humans that could influence the resource utilisation or throughput rates as part of our current research

Towards a Formal Model of Human Workflow

Abstract. BPEL (Business Process Execution Language) has become the standard for specifying and executing workflow specifications for web service composition invocation. A major weakness of BPEL is the lack of so-called “human workflow ” support. The BPEL4People specification tries to amend this by adding human task support to BPEL. In this paper, we propose a formal model of BPEL4People using the CSP process algebra, and discuss some issues we found through analyzing the model. Although based on BPEL4People, this is a general work, and can also be viewed as a formal model of human workflow.