Cloud computing is a new trend in information technology that provides resources and shares services by web services over the internet for users. Many web services have similar functionality with different quality of service (QoS) in the cloud. Thus, an appropriate service composition method is needed to assign an optimal composition of services to the users. Furthermore, service level agreement (SLA) which is the level of service expected from the service provider should be satisfied by the service composition method that less considered in previous studies. Introducing an appropriate algorithm for web service composition that could achieve high QoS while satisfying SLA constrains is one of the main issues in the cloud computing area. In this study, an improved multi-verse optimization algorithm for web service composition that is called IMVO algorithm is proposed to improve QoS while satisfying SLA. The simulation results show increasing of normalized QoS up to 57% in comparison with the other approaches, especially for service composition problems with SLA.

云计算是信息技术的新趋势，它通过Web服务为用户提供资源并通过Web服务共享服务。许多Web服务在云中具有类似的功能，但具有不同的服务质量（QoS）。因此，需要适当的服务组合方法来将最佳服务组合分配给用户。此外，应通过服务组合方法来满足服务水平协议（SLA），即服务提供商所期望的服务水平，该方法在以前的研究中很少考虑。为网络服务组合引入合适的算法，该算法可以在满足SLA约束的同时实现高QoS，这是云计算领域的主要问题之一。在这个研究中，提出一种改进的用于Web服务组合的多版本优化算法，称为IMVO算法，以在满足SLA的同时提高QoS。仿真结果表明，与其他方法相比，归一化QoS提高了57％，尤其是对于SLA的服务组合问题。