XXXX-as-a-Service aaS

The context of the utility to an as-a-Service capability in IT relies heavily on where the demarcation of use resolves.

It's much easier to see it in a graphical depiction.

In general, Infrastructure and a portion of the virtualization/abstraction are what will be acted upon by nearly all use cases (if we forgo the licensing issues with respect to those things more appropriately economical on bare metal).

On top of that you'd build out the as-a-Service for Infrastructure, which at the base level is virtualization/abstraction/operating system automation and management. 

Then you walk up the technology chain, including the management of constructs necessary for applications to be automated in build / test and delivery.

The last step on the technology chain is the delivery of what should be the most important element (though even today, we've people worried about HOW the underlying physical elements are doing), the Application delivery.

Tiers of 'as-a-Service' delivery