According to different levels of services in the Cloud, and inspired by the taxonomy of “Everything As A Service” (XaaS), Cloud services can be categories as Infrastructure As A Service (IaaS), Platform As A Service (PaaS), and Software As A Service (SaaS).

1)    Infrastructure as a Service provisions hardware and equipments which can be accessed through a standard API to deliver software application environment with a on-demand resource usage-based pricing model. Infrastructure, including computational power,  storage, network and sometimes legacy system can be required on-demand or scaled up and down as the need of applications , and be charged on usage. These features of IaaS are enabled by hardware virtualization, resource monitoring, and usage metering.

2)    Platform as a Service offers developer with a high-level integrated environment to build, test, and deploy custom applications. Services in PaaS can be categorized into Programming Environment and Execution Environments . An Execution Environment PaaS typically encompasses a Programming Environment. Most commercialized implementations of PaaS are design for hosting Web applications, such as Google’s App Engine, and Microsoft Azure. Developers of these PaaS accept some restrictions on the type of software, use hundreds of readily available tools and services, and build quickly scalable applications. To the concept of Ubiquitous Cloud, users can use data from remote sensors and control remote devices like a virtually local devices through a standard Web service interfaces or even deploy user’s application onto the PaaS.

3)    Software as a Service is a software-delivery mode . The software vendor delivers software as utility services and charges on a per-use basis. And users subscribe to such a service and execute it on-demand through some form of client-side architecture via the Internet or Intranet. One of the most famous SaaS stockholder is Slaesforce.com who delivery Customer Relationship management (CRM) Services.

SaaS enables effective and efficient delivery of software systems as services. SOA and Web services can transform existing software systems into Web services, which can be access by programs and integrated into other business process. Traditional service providers , such as Google, Amazon.com, and PayPal have been working delivering Web services, which enable software users can access their service without going through Web pages via standard Web service interfaces.

In ubiquitous computing domain, especially for global smart spaces, raw data, integrated data, control power of remote devices, and value-added services can all be delivered as services of various granularities. In iTransIT framework, highlighted software resources are information ranging from places of interest, to prevailing road and weather conditions, to expected journey times, to up-to-date public transport information, to enable privileged users to interact with the infrastructure. All this software can be transformed to Web services and delivered as SaaS.

Reference:

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