In this paper, we propose a novel approach for flexible representation of complex timing constraints for scheduling real-time tasks under different scheduling paradigms. It allows different instantiations of the task attributes, depending on which underlying scheduling policy is used. Scheduling parameters are flexibly derived from original timing constrains, rather than using the same set of task attributes for all schedulers. For each real-time task in the system, temporal feasibility windows are identified, such that if the task executes and completes within its feasibility window, the original timing constraints will be met. Then, scheduler dependent parameters are derived to guarantee the tasks' execution and completion within their feasibility windows.