关键词: 网格计算，工作流调度，QoS约束，双向分层

Abstract: In order to meet user's QoS rectuirement for the implementation of grid workflow, the key tasks of the workflow were analyzed firstly, and the QoS of the whole workflow was divided into segments which are the QoS-constrained of a single task. Then,a grid workflow scheduling algorithm (Q-TWS) based on Two-Way Stratified was proposed.Through both positive layering and reverse layering, this algorithm can find the parallel relation between tasks easily and accurately. Q-TWS can relax the task execution time, increase flexibility scheduling and meet user QoS requiremenu. Simulation results show that Q-TWS has a shorted execution time and a less execution cost compared with BL when the two algorithms have the same deadline.

Key words: Grid computing, Workflow scheduling, QoS-constraincd, Two-way stratified