The three service models SaaS-PaaS-IaaS together are referred to as theSPI model of cloud computing. In this layered architecture of the cloud service model, by moving upward, each service layer is empowered by the capabilities of the service layer(s) beneath it. Thus, PaaS is empowered by the IaaS layer and SaaS is empowered with the potential of underlying IaaS and PaaS layers. Figure 5.8 shows the layered cloud SPI model with the mention of popular commercial services. One point to note here is that there is no functional relation between cloud deployment models and delivery models. Any delivery model can exist in any deployment scenario and any delivery/deployment pairing is possible. Although, SaaS offerings are mostly public services and hence the SaaS/public combination is more common than the other combinations.
The three service models SaaS-PaaS-IaaS together are referred to as theSPI model of cloud computing. In this layered architecture of the cloud service model, by moving upward, each service layer is empowered by the capabilities of the service layer(s) beneath it. Thus, PaaS is empowered by the IaaS layer and SaaS is empowered with the potential of underlying IaaS and PaaS layers. Figure 5.8 shows the layered cloud SPI model with the mention of popular commercial services. One point to note here is that there is no functional relation between cloud deployment models and delivery models. Any delivery model can exist in any deployment scenario and any delivery/deployment pairing is possible. Although, SaaS offerings are mostly public services and hence the SaaS/public combination is more common than the other combinations.