Information Technology Reference
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customization. Due to the early stage of development of Internet and Web tech-
nology, application service providers were not able to scale flexibly and to provide
reliable and robust services. Further reasons for the failure of ASP have been: the
centralized approach for computing, which requires the sending of input and output
data, and the general lack of trust in the ASP paradigm (Xu and Seltsikas 2002,
Desai and Currie 2003, Mittilä and Lehtinen 2005).
At present, Grid Computing and ASP are converging towards SaaS. The acronym
SaaS is reported to have been coined in the white paper “Strategic Backgrounder:
Software as a Service” published by the Software & Information Industry's (SIIA)
eBusiness Division in 2001 (SIIA 2001, Wikipedia 2009c) and denotes a new evolu-
tionary step in delivering of software as a service based on Web Services and Grid
technology.
The convergence of Web Services and Grid Computing technology provides
new opportunities to solve the ASP delivery problems (Xu and Seltsikas 2002,
Mittilä and Lehtinen 2005). Web Services enable the modularization of applications
in several services that can be combined and customized by users. Grid technology
has the potential to provide the necessary flexibility and scalability on the infra-
structure side of SaaS offerings. As already described in the previous sections, Grid
Computing bundles heterogeneous pools of computing resources, storage systems
and networks into a virtualized system that appears to applications as one single, but
at the same time scalable and flexible computing entity. The applications deployed
on a Grid are flexible and scalable and can be offered in modularized manner. With
the help of Grid, the ASP business model is evolving from one-to many to a many-
to-many model, where several service offerings are bundled and can flexibly be
obtained by the user (Desai and Currie 2003).
Another converging tendency between Grid Computing and software applica-
tions is the shift towards Grid-enabled applications. The term
Grid-enabled appli-
cation
is used to denote software applications, usually offered on the market as
pre-packaged software, that are extended in a way that they can run in a distributed
manner in a Grid environment. To Grid-enable a pre-packaged software product
therefore means that a previously pre-packaged centralized application is enabled
to run either on a distributed Grid infrastructure or to be offered as an online service
based on the Software as a Service (SaaS) paradigm (see also Sanjeepan et al. 2005).
3.6.3 The Evolution Towards Cloud Computing
The previous two sections have sketched the current trends in computing. Grid
Computing as technology is maturing. With Grid Computing the integration of
heterogeneous physical resources into one virtualized and centrally accessible
computing unit has become possible. Based on the convergence with SOC, Grid
Computing is offered in form of Grid services that can flexibly be used by applica-
tion developers that would like to deploy their application on a Grid Infrastructure.
Maturing Grid technology is enabling new business models of utility computing, i.e.
providing computing power on demand on a pay-per-use basis. While the develop-
ments in Grid technology are basically pushed by hardware and system software
