Cloud service models are generally classified based on the type of resources shared, as SaaS (stands for Software as a Service), PaaS (stands for Platform as a Service) and IaaS (stands for Infrastructure as a Service). Cloud deployment models include public, private, hybrid and community cloud models.
IAAS (STANDS FOR INFRASTRUCTURE AS A SERVICE)
The type of resources shared in IaaS mainly includes physical servers, virtual machines, load balancers, IP addresses and virtual local area networks (VLANs); but often also includes other resources such as a virtual-machine disk image library, raw (block) and file-based storage, firewalls and even software bundles.
Cloud providers typically bill IaaS services on a utility computing basis; cost reflects the amount of resources allocated and consumed. Examples includes Amazon Web Services (AWS) such Amazon EC2 for computing capacity and Amazon S3 for cloud storage, and Dropbox etc.
PAAS (STANDS FOR PLATFORM AS A SERVICE)
The type of resource shared in PaaS is usually a computing platform, typically including operating system, programming language execution environment, database, and web server. Application developers can develop and run their software solutions on the cloud platform without the cost and complexity of buying and managing the underlying hardware and software layers.
With some PaaS offerings, the underlying computer and storage resources scale automatically to match application demand so that the cloud user does not have to allocate resources manually.
Examples include Windows Azure, force.com from salesforce and Google App Engine.
The iPaaS, which stands for integration Platform as a Service, is a sub type of PaaS and deals with integrating various cloud technologies. Examples of iPaas include Dell Boomi AtomSphere from Dell and CloudStreams from Software AG. I have worked with Dell Boomi AtomSphere previously.
SAAS (STANDS FOR SOFTWARE AS A SERVICE)
The type of resource shared in SaaS includes application software and databases. Cloud providers manage the infrastructure and platforms that run the applications. SaaS is sometimes referred to as “on-demand software” and is usually priced on a pay-per-use basis. SaaS providers generally price applications using a subscription fee.
Examples includes Salesforce CRM, SuccessFactors, Office 365 from Microsoft, Ariba Buyer On Demand and most Google services such as Gmail, Google Apps etc. I have worked as a product developer for ‘Ariba Buyer On Demand’ product when I was working with Ariba, an SAP Company.