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hard working weekend with PHP on a machine God
knows where it is’’, i.e, Platform is as a Service [17].
D. A computer scientist’s view
Scientists investigate cloud computing into “We are
not programming a single machine, rather the World
Wide Computer’’. It means infrastructure is as a Service
E. An economist’s view
Economically, “The most interesting thing about the
cloud computing is not the technology, but the new
evolving social standards and business models, and the
ramifications of egalitarianism on a global scale’’.
Everything he thinks is as a Service.
Based on our understanding of the essence of what
Clouds are promising to be, we propose that Cloud
computing is a usage model in which resources are
deliveries and, it means to provide resources, such as
hardware, software and applications as scalable and "ondemand"
services via public network in a multi-tenant
environment. The providing resource network is called
‘Cloud’. All resources in the ‘Cloud’ are used whenever
as utility and scalable infinitely.
Ⅲ. THREE LAYERS OF CLOUD COMPUTING
Cloud computing is generally related to three different
levels as follows.
A. Software as a Service: SAAS
Software as a Service delivers special-purpose
software which is remotely accessible by consumers via
the Internet with a usage-based pricing model. Salesforce
Customer Relationships Management (CRM) system [7]
and Google Apps [8] are two examples of SaaS.
Moreover, Microsoft’s Live Mesh allows files and folders
to be shared, and synchronized across multiple devices.
B. Platform as a Service: PAAS
Platform as a Service provides a high-level integrated
environment to design, build, test, deploy and update
online custom applications. A typical example is
Google’s App Engine [9], which enables customers to
build Web applications on the same scalable systems
which power Google applications. Another example is
SalesForce Apex language that allows the developers of
the cloud applications to design, along with their
applications' logic, their page layout, workflow, and
customer reports. In this respect, a Hadoop [11]
deployment on the cloud would be considered a cloud
software environment, as it provides its applications'
developers with a programming environment, i.e. map
reduce framework for the cloud. Similarly, Yahoo's Pig
[12], a high-level language to enable processing of very
large files on the hadoop environment, may be viewed as
an open-source implementation of the cloud platform
layer.
C. Infrastructure as a Service: IAAS
Infrastructure as a Service offers hardware, software,
and equipments which are mostly at the unified resource
layer or part of the fabric layer, to deliver software
application environments with a resource usage-based
pricing model. Infrastructure can scale up and down
dynamically based on application resource needs.
Amazon's Elastic Compute Cloud (EC2 [13]), and
Enomalism elastic computing infrastructure [14] are
arguably the two most popular examples of commercial
systems available in this cloud category. In this space,
there are also several academic open-source cloud
projects, such as Eucalyptus [15].
Some examples of data storage systems are: distributed
file systems (e.g., GFS), replicated relational databases
(RDBMS) and key-value stores. RDBMS, for example
opt to present a stricter consistency model at the cost of
the availability of the data, while key-value stores have
placed more importance on the availability of the data
while relaxing the consistency model for the storage.
Although user interface to the cloud infrastructure
components varies substantially from one system to
another, SOAP and REST are two examples of interface
protocols used with some cloud computational resources.
Ⅳ. SOME CLOUD COMPUTING PLATFORMS
Industry analysts have made bullish projections on
how Cloud computing will transform the entire
computing industry.
A. Microsoft’s Windows Azure platform
Microsoft’s Windows Azure platform is a group of
cloud technologies, each providing a specific set of
services to application developers. This platform can be
used both by applications running in the cloud and by
applications running on local systems [1]. It contains the
following components and is shown in Figure 1.
• Windows Azure: A Windows-based environment
for running applications in Microsoft data centers.
• SQL Azure: SQL Server based data services.
• .NET Services: Distributed infrastructure services
to cloud-based and local applications.
Figure 1. The Windows Azure platform
1) WINDOWS AZURE
Windows Azure runs on a large number of machines,
all located in Microsoft data centers and accessible via
the Internet. A common Windows Azure fabric knits this
plethora of processing power into a unified whole.
Windows Azure compute and storage services are built
on top of this fabric.
2) SQL AZURE
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