# Evaluation of Cloud Services: A Fuzzy Multi-Criteria Group Decision Making Method +
## 2 The Cloud Service Performance Evaluation and Selection Problem  
Cloud computing is widely used to enable individual organizations to access specific information technologies at a much lower cost. It allows these organizations to rapidly expand their operations by giving them the ability to quickly and cost-effectively roll-out new products and services, and at the same time, serve their customers better across the world [11]. Furthermore, the adoption of Cloud computing can lead to (a) the reduction in initial capital expenditure [12]; (b) minimal management [1]; (c) optimized resources utilization [13; 14]; and (d) improved energy efficiency [15], increased scalability, increased agility, reduction of information technology infrastructure complexity, and improved alignment between businesses and information technology services [16]. There is an upward trend in the adoption of Cloud computing [17; 18]. A KPMG survey [19] reveals that 81% of organizations are either planning their initial forays, are in the early stage of implementation, or have a full implementation of Cloud computing. Many organizations have started building applications on the Cloud infrastructure and making their businesses agile by using flexible and elastic Cloud services [4]. Moving applications and data into the Cloud, however, is not a straightforward process. This is because numerous challenges exist to leverage the full potential that Cloud computing can offer. With the growth of public Cloud service offerings, it has become increasingly difficult for Cloud service customers to decide which provider(s) can fulfill their requirements for quality Cloud services [1]. For example, each Cloud service might offer similar services at different prices and performance levels with different sets of features. While one provider might be cheaper for storage services, they may be more expensive for computation. Given the diversity of Cloud service offerings, it is an important challenge for organizations to discover the suitable Cloud providers who can satisfy their requirements. There may be trade-offs between different user requirements fulfilled by different Cloud service providers. As a result, it is not sufficient to just discover multiple Cloud services. It is important to determine the most suitable Cloud service through a comprehensive performance evaluation in a specific situation [3]. The performance evaluation of available Cloud services with respect to a set of specific criteria is complex [20]. This is due to the presence of the multi-dimensional nature of the evaluation process and the presence of vagueness of the decision making process [21]. To effectively deal with this problem, an overall evaluation of individual Cloud services is desirable. In order to adequately measure the performance of the available Cloud services, it is important to first define the suitable criteria for ensuring that the evaluation and selection process produces an accurate and effective outcome for specific organizations. Much research has been done on identifying the relevant criteria for evaluating the performance of Cloud services [1; 3; 5; 6; 8; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22]. A review of the related literature leads to the classification of the evaluation criteria into (a) security, (b) performance, (c) accessibility, (d) usability, (e) scalability, and (f) adaptability. Figure 1 shows the hierarchical structure of the Cloud service performance evaluation problem. Security (C1) refers to the ability of a Cloud service to protect the organizational data in terms of their confidentiality and privacy. It is one of the major concerns for organizations when they consider moving their businesses to a Cloud environment. There is a great deal of uncertainty and risks related to the use of networks, hosts, applications, and data in the adoption of Cloud services. Figure 1: The hierarchical structure of the Cloud service performance evaluation problem.