Extending execution plan with execution path set partitions

Abstract

Due to the increase in web services, non-functional or QoS parameters have been widely addressed. QoS-aware service selection is commonly formulated as an optimization problem aimed at achieving the execution plan that optimize the overall QoS parameter of the composed application while satisfying all the constraints on individual QoS parameters and considering all of the possible execution scenarios. In existing work, execution plans commonly assign one service for each task. For composed applications containing exclusive branches, some tasks may appear in multiple execution scenarios. Unfortunately, since one-fit-all services for these tasks considering every execution scenario are not always available, execution plans have to make compromise. As a result, when some users have strict QoS constraints, feasible execution plans may not exist for the composed application but exist for every execution scenario. This problem becomes more important and challenging for self-adaptive systems, due to the overhead of unwanted runtime adaptations. In this paper, we breaking such one-one mapping between services and tasks. We provide methods to divide all execution scenarios a task involved into exclusive groups (i.e. execution path set partitions) and show that a distinct service can be bound to this task for each group without causing any confusion. In order to find the optimal execution plan, we modify existing MILP based approaches to cooperate with our method. We also evaluate our approach experimentally using real dataset.The results show that it is more flexible, robust to QoS constraints, and can possibly improve the overall QoS associated with the optimal execution plan.