1 Introduction
Due to the diversity and dynamic nature of cloud services, selecting the most suitable cloud service has become a major issue for potential cloud consumers. Prior to cloud service selection, an evaluation of cloud services should be performed first. There are two types of approaches which can be used to conduct such an evaluation. The first type of approaches is based on objective performance assessment from ordinary QoS parameters (Quality-of-Service, e.g., service response time, availability and throughput) [1], [2], [3] and predesigned benchmark testing [4], [5], [6]. As cloud services are highly virtualized, some methods and tools for traditional IT computation measurements can be appropriately applied in cloud environments. By combining these methods and tools according to the characteristics of cloud services, many metrics can be quantitatively assessed (e.g., the speed of CPU and I/O). The second type of approaches is based on ordinary consumers’ (OCs) subjective assessments extracted from their subjective ratings for every concerned aspect of cloud services [7], [8]. In this type of approaches, cloud services are usually treated like traditional web services, thus some rating-based reputation systems [9], [10], [11] can be utilized for cloud service selection.