Service models

IT-services are offered as services.

Cloud computing can be separated into three models are theoretically built on each other. (see Krutz, Roland; Vines, Russell Dean 2010, p 24)

The lower level is Infrastructure-as-a-Service (IaaS), that includes a basic infrastructure, such as computing, storage and communication services.
Platform-as-a-Service (PaaS) is based on that model, which already offers an overall managed environment. The customer only takes care about the software design of the platform.

The most abstract service model is Software-as-a-Service (SaaS), which contains the complete applications. The user can make use of the applications as needed. (see Meir-Huber, Mario 2010, p 42)