I've read:IaaS, PaaS and SaaS Terms Clearly Explained and Defined andCloud Computing  Demystifying SaaS, PaaS and IaaSAnd I've got 2 questions:Is Google App Engine considered PaaS or IaaS?Is HaaS a subset of IaaS or is HaaS really just another name for IaaS?
SaaS / PaaS / IaaS / HaaS
web services;google app engine
This answer is from an article that I read Toward a Unified Ontology of Cloud Computing  As Google App Engine gives you a platform for better utilization of Google's resources, it can be considered PaaS. A good key for me is Is this environment giving me some kind of API for better integration with a system? Then it's PaaS.I read more than one definition about this, but nowadays what sounds better to me, and what the article writer says, is that HaaS, like CaaS (communication as a service) is a subset of IaaS: they create the infrastructure needed to perform IaaS, but it can't be considered essentially service like IaaS.Here is a figure that describes what I'm saying: