Abstract

Project schedules are subject to change due to uncertain aspects, such as failure of machines, worker Absenteeism and turnovers, changes of scope, and reworks, etc. These changes may often result in project delays, cost overruns, quality defects and other negative impacts. In response to changes, project managers need to revise the schedule to minimize the impact of the changes. They usually revise the schedule by modifying allocation of resources and arrangement of tasks to cope with the changes. In general, it is extremely difficult to modify a schedule due to limited resources, extensive interaction among activities and resources besides the typical constraints. The problem remains in how to control and minimize the overall impact of changes by taking necessary corrective actions.
In the above context, we first introduce a standard model for task-resource allocation schedule that incorporates necessary relationships among tasks and resources, and possible constraints of the project. We then propose a reactive scheduling approach to modify the baseline schedule to address changes due to the absence of workers during project execution. To modify the schedule, we define three change options based on preemptive and non-preemptive resource reassignment strategies. When a change occurs, the reactive scheduling framework selects the best change option using systematic decision process by capturing the change scenario and assessing the change impact. The change impact is measured in view of the importance of absent worker, length of absence, and criticality of affected tasks. The objective of this approach is to limit the increasing of the project duration from initial deadline (i.e., delay) without changing too many task-resource assignments. Finally, an example application related to software development project is presented to illustrate the implementation and features of our proposed approach.