# Evaluation of Cloud Services: A Fuzzy Multi-Criteria Group Decision Making Method +
## 2 The Cloud Service Performance Evaluation and Selection Problem
Hosting data under another organization's control is always a critical issue which requires stringent security policies employed by the Cloud service provider. [PERSON] et al. [22] and [PERSON] et al [23] believe that the support and maintenance provided by the Cloud services provider and the security of the system are the main factors to be used for the selection of the most suitable Cloud service. [PERSON] and [PERSON] [8] state that a positive user perception of the level of security and privacy of a specific Cloud service positively influences the actual selection of such a service in the real world. [PERSON] et al. [3] point out that there is a significant relationship between the level of the security and privacy concerns and a willingness to provide personal and sensitive information. [PERSON] and [PERSON] [24] state that, due to the concept of resource pooling with other Clouds, the clients' data is available both to the third-party Cloud and the Cloud in use. [PERSON] and [PERSON] [25] state that an acceptance of the Cloud services is largely affected by the security, perceived mobility, quality of the service, connectedness, and satisfaction of individual users in the evaluation and selection process. This shows that security is a critical criterion for evaluating the appropriateness of Cloud service for implementation. Performance (\(C_{2}\)) is used to measure the quality of the service that a Cloud service provides. There are many different solutions that a Cloud service can provide for addressing the needs of different organizations. It is therefore important for individual organizations to understand how their applications perform on the different Clouds and whether these application deployments meet their expectations [3; 5; 26]. [PERSON] and [PERSON] [27] show that organizations need to understand how their applications perform on different Clouds and whether these applications meet their expectations and requirements for achieving the competitive position in the market place. [PERSON] et al. [28] claim that the performance of the Cloud service is important for improving the operational effectiveness of an organization. Service accessibility and usability (\(C_{3}\)) refers to the simplicity of the use of a Cloud service for supporting the business operations. The easier it is to use a Cloud service, the faster an organization can switch to it [5; 21]. [PERSON] and [PERSON] [29] state that a Cloud service needs to enhance the accessibility to many information resources which are locked either in proprietary or inaccessible desktop applications. [PERSON] et al. [30] believe that the usability of a Cloud service should include multiple factors such as accessibility, learnability, and operability of a Cloud service. Scalability (\(C_{4}\)) refers to the ability of a Cloud service to fit a problem as the scope of that problem increases. It depends on the automatic resizing and reconfiguration of Cloud resources [6]. The focus here is on how the Cloud service has the ability to make good use of available resources at different workload levels to avoid an excessive delay and unproductive consumption of organizational resources. [PERSON] et al. [3] state that the scalability of a Cloud service is an important quality measure for an organization who wants to move to the Cloud. This is because the costs of using a Cloud service increase, particularly at peak times if the Cloud does not allow an application to scale well vertically. [PERSON] and [PERSON] [5] believe that a Cloud service should have the ability to be scaled up to easily meet the demand through replication and distribution of the requests across a pool or farm of available servers in a specific situation. Adaptability (\(C_{5}\)) reflects on the ability of the Cloud service to adjust the services based on customers' requests [1; 5; 21; 31; 32]. [PERSON] et al. [6] and [PERSON] et al. [33] state that Cloud services should be able to create a pool of resources that are flexible enough to handle many different sorts of applications.