Information Technology Reference
In-Depth Information
As a consequence of the requirement for an easy and abstracted access to the
physical layer of a Cloud, virtualization of the physical layer and programming plat-
forms for developers emerged as major features of Clouds.
4.3.2.2 Platform as a Service (PaaS)
Platforms are an abstraction layer between the software applications (SaaS) and
the virtualized infrastructure (IaaS). PaaS offerings are targeted at software devel-
opers. Developers can write their applications according to the specifications of a
particular platform without needing to worry about the underlying hardware infra-
structure (IaaS). Developers upload their application code to a platform, which
then typically manages the automatic upscaling when the usage of the application
grows (RightScale 2008). PaaS offerings can cover all phases of software develop-
ment or may be specialized around a specific area like content management (Sun
2009a). Examples are the Google App Engine, which allows applications to be run
on Google's infrastructure, and Salesforce's Force.com platform. The PaaS layer
of a Cloud relies on the standardized interface of the IaaS layer that virtualizes the
access to the available resources and it provides standardized interfaces and a devel-
opment platform for the SaaS layer.
4.3.2.3 Software as a Service (SaaS)
As explained in section 3.6.2 in chapter 3, SaaS is software that is owned, delivered
and managed remotely by one or more providers and that is offered in a pay-per-use
manner (see also Mertz 2007). SaaS is the most visible layer of Cloud Computing
for end-users, because it is about the actual software applications that are accessed
and used.
From the perspective of the user, obtaining software as a service is mainly moti-
vated by cost advantages due to the utility-based payment model, i.e. no up-front
infrastructure investment. Well known examples for SaaS offerings are Salesforce.
com and Google Apps such as Google Mail and Google Docs and Spreadsheets.
The typical user of a SaaS offering usually has neither knowledge nor control
about the underlying infrastructure (Eymann 2008), be it the software platform
which the SaaS offering is based on (PaaS) or the actual hardware infrastructure
(IaaS). However, these layers are very relevant for the SaaS provider because they
are necessary and can be outsourced. For example, a SaaS application can be devel-
oped on an existing platform and run on infrastructure of a third party. Obtaining
platforms as well as infrastructure as a service is attractive for SaaS providers as it
can alleviate them from heavy license or infrastructure investment costs and keeps
them flexible. It also allows them to focus on their core competencies. This is similar
to the benefits that motivate SaaS users to obtain software as a service.
According to market analysts, the growing openness of companies for SaaS
and the high pressure to reduce IT costs are major drivers for a high demand and
growth of SaaS, and by that also for Cloud Computing, in the next years. In August
2007, analyst firm Gartner forecasted an average annual growth rate of worldwide
SaaS revenue for enterprise application software of 22.1% through 2011, reaching a
