om service APIs, refer to Section 2.2. In addition to those above-mentioned concepts, various others are emerging in the light of the cloud business opportunities, like Communication as a Service, Database as a Service, Desktop as a Service, and alike, transferring the trend into Everything as a Service. 4.3.2 Cloud Computing: IT-Based Service Delivery Business Considering the various business opportunities for large enterprises, small-medium business, for customer support or internal usage, for large-scale consumer market- three types of cloud for IT-based service delivery can be identified: Private cloud is a corporate system emulating a cloud environment in private networks to deliver applications and services to users (e.g., employees or business partner). It can be provided by a third-party provider, or network operators. The important aspect is that all resources within a private cloud are not shared with any external customer. It uses technologies to reduce the customer's opex, for example, by virtualization, and dynamic provisioning with special appliance to the private setting requirements. The effort to host and operate private clouds fits well in large enterprises aiming to optimize their own IT systems (for cost, centralized service management, etc.) Public cloud is a system that provides dynamic resource provisioning on a self- service on-demand basis over the Internet. The resources (hardware, software, ser- vices) are accessed over Web portals. Applications can be offered for free or a minimal fee when provisioned via the providers Web site. Those resources are nor- mally addressed to the consumer or Small-Medium Enterprise Business (SMB) users, and in nature accessed in an ad hoc manner. On the other hand, resources can also be accessed on a contract basis via a defined sign-in mode. This is normally applied in SaaS business models, where parameters like service quality, provision- ing, or guaranteed availability is defined by policies in the form of Service Level Agreements (SLA). Hybrid cloud is