# A Trusted Multi-Cloud Brokerage System for Validating Cloud Services Using Ranking Heuristics
## 2 Literature Review  
[PERSON] et al. [3] proposed a review work on cloud brokers in a multi-cloud environment. The authors put forth a valid argument, that the available cloud brokers were not suited to the heterogeneous environment. In addition to that, energy consumption has been accounted for and highlighted in their work. However, the paper failed to address the possible techniques to overcome the identified issues. [PERSON] et al. [4] highlighted the usages of a cloud broker in an interconnected cloud computing environment. Through this study, the authors have analyzed the strengths and weaknesses of the cloud broker in the areas such as pricing, optimization, trust, and QoS. Since the paper is a survey, deeper discussion only focused on better understanding of cloud broker in the multi-cloud environment. [PERSON] et al. [5] mentioned the various roles of cloud service brokers such as intermediation, aggregation, arbitration, integration, and customization. Hence, the service delivery process is entirely coordinated by cloud service providers, the cloud service broker, and the customers. Supposing that there is an issue in any one of the involved parties, it will certainly affect the performance of the broker. [PERSON] [6] addressed the need for interoperability between the clouds, since the clouds are locked in by vendors and need to be combined to fulfill the cloud user's requirements. Though we currently have hybrid-type clouds, it is mandatory to interlink the multiple clouds for the better performance and user satisfaction. Hence, the authors proposed an approach to provide features such as portability and interoperability among multiple cloud providers. But this proposal does not highlight the practical approach to resolving the issues of the interoperability between the cloud service providers. Similarly, the authors in [7] also addressed the problem of service composition in multi-cloud environments. They also focused specifically on interoperability issues while performing multi-cloud service composition. In some situations, the reasoning is more difficult due to the nature of complex user requirements and the heterogeneity of cloud services. Hence, it is necessary to upgrade the entire system using parallel programming models. In another work [8], the authors addressed the interoperability and portability problems of cloud architectures. Cloud ontology-based service discovery and selection has been carried out to resolve the interoperability and portability problems in a cloud environment. In addition, [PERSON] et al. [9] performed the service selection with the support of constructed cloud ontology. A semantic network-based approach with the intersection search concept is advocated to perform the service selection. [PERSON] et al. [10] discussed the limitations of the single cloud provider in the process of service offering. According to the increase in the demand of services, the existing approaches suffered in two aspects, such as SLA and QoS. Hence, the authors proposed an inter-cloud framework with the support of agents. The agents are responsible for publishing, discovering, and providing the services to the cloud user with agreed SLA. However, the decision-making policies for buying and selling services are not addressed in this paper. [PERSON] and [PERSON] [11] presented a review to emphasize the necessity of an inter-cloud architecture to accomplish reliability, Quality of Service (QoS), and cost efficiency by exploiting multiple clouds. The authors proposed the classifications for inter-cloud architectures and brokering apparatuses. The cloud environments that facilitate the brokering of distributed applications were also discussed. [PERSON] et al. [12] presented a review on the use of SLA-based brokering for inter-cloud computing which focused on QoS. In this work, the authors have elaborated on some of the SLA-based brokers and their workflow. All kinds of basic information on the aspects of the broker are explained theoretically.