# Ontologies in Cloud Computing--Review and Future Directions
## 2 Background and Related Work
### Deployment Models  
The deployment model (irrespective of the service model) is divided into five categories of clouds, namely: Private, Public, and Hybrid Cloud, with the shared concept called community cloud and the multi-cloud [1; 16]. Private cloud is one where computing access is confined within the organization. Its operations are based on a pool of shared resources. It should be noted that this cloud model is entirely operated and managed in-house by the organization's IT specialist(s), and access to resources is over a secured intranet. **Advantages of the private cloud:**  
1. Enhanced control: the proprietor controls access in and out of the network, sets the security policies and regulates user behavior. 2. Security and Privacy: improved access and security is possible when resources are segmented within the same infrastructure. 3. Tailored: solutions are modified to meet the company's specific need. **Disadvantage of the private cloud:**  
1. Controlled scalability: this cloud model has limitations on scalability because it is a function of underlying hardware. It is scaled within the resource capability of the owners. 2. Hugh budget: the overhead is higher compared to public cloud since the owner would be expected to pay for every resource at his disposal. Public cloud is one where cloud services are provided as open access for the public [2; 16]. Since the public cloud is opened to just anybody, the security cannot be guaranteed; in the public cloud, infrastructural services are offered over the internet. This arrangement gives ownership to the vendor and not the client. **Advantages of the public cloud:**  
1. Marginal Investment: it is a good option for users in need of instant cloud service, it has little or no advance payment as it is a pay-as-you-go service model. 2. Initial capital outlay: the client is not bordered about the hardware infrastructural setup as this is borne by the vendor. 3. Management is not an option: the client does not concern itself with managing the public cloud infrastructure. 4. Scalability: the system has the capacity to respond to clients' resource needs at any time. **Disadvantages of the public cloud:**  
1. Security and Privacy: due to public access, its protective capacities against criminals are weak. 2. Reliability: The system is vulnerable to failures mainly due to increased traffic from several clients. Hybrid cloud is the merging of private and public clouds, in which offerings from each domain are absorbed in a combined manner, having some relationships with some external service providers [17]. **Advantages of the hybrid cloud:**  
1. Robust and control: with flexibility, it is possible to create a solution to meet your business need on-demand. 2. Budget: there is a reduction in cost due to the merger between private and public clouds; this is because public cloud offers free scalability. Therefore, depending on the task at hand, there may or may not be any cost attached. 3. Security: data integrity is guaranteed to a very large extent due to proper data segregation. **Disadvantage of the hybrid cloud:**  
1. Maintenance: they may need for extra cost on maintenance when using the hybrid cloud model. * Difficult Integration: the process of integration may become complex when attempting to integrate two dissimilar models. Community cloud is a cloud facility reserved for a specific community's usage based on organizations with a shared interest. It could be managed individually or by more members of the organization, and it can be situated on-site or off-site. **Advantages of the community cloud:**  
* Effective budget: overhead is light since numerous groups take responsibility for sharing the cloud. * Shared resources: it provides the platform to share cloud resources and infrastructure, which in turn reduces cost of running and maintenance. **Disadvantages of the community cloud:**  
* Restriction on bandwidth: there is a fixed bandwidth and data storage within the organization or individual within the community.