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Defining Cloud Computing
Irena Bojanova
Founding Chair, IEEE CS Cloud Computing STC – join at
Associate Editor, IEEE Transactions on Cloud Computing
Editor, IEEE CS IT Professional
Professor, UMUC
FEB 24, 2013 12:00 PM
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painting of cowboy wrangling wild horses
It's the High-Tech Wild, Wild West out there!
Although the Cloud Computing marketplace is still chaotic, it is:
  • Exciting
  • Fast-growing
  • Full of opportunities

Cloud computing (CC) allows pay-per-use or charge-per-use access to applications, software development and deployment environments, and computing infrastructure. It provides optimized and efficient computing through enhanced collaboration, agility, scalability, and availability. Some formal definitions of CC are as follows.

NIST (2009): Cloud computing is a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.

Note: NIST posted the 15th version of their definition of CC in July 2009. After vetting with government and industry, it was posted for public comments in January 2011, and the final version was published in September 2011.

European Union (2010): A 'cloud' is an elastic execution environment of resources involving multiple stakeholders and providing a metered service at multiple granularities for a specified level of quality (of service).

Gartner: A style of computing, whose massively scalable and elastic IT-related capabilities are provided as a service to external customers using Internet technologies.

The NIST definition though is the most precise and in 2012 EU also referred to it. The NIST Cloud Model is composed of five essential characteristics, three service models, and four deployment models – the CSA visual form is provided on Figure 1. and concise explanations are provided in the three tables that follow.

Figure1. The Cloud Model
Table 1. Cloud Characteristics

Cloud Characteristic


On-demand self-service

Computing capabilities (e.g. server time and network storage) can be unilaterally automatically provisioned as needed.

Broad network access

Capabilities are accessible through heterogeneous thin or thick client platforms (e.g., mobile phones, tablets, laptops, and workstations).

Resource pooling

Computing resources (e.g. storage, processing, memory, and bandwidth) are pooled to serve multiple consumers, dynamically assigned and reassigned according to demands. Customers have no control over exact location of resources, but may be able to specify location (e.g., country, state, or datacenter).

Rapid elasticity

Capabilities can be elastically provisioned and released to commensurate with demand. Available capabilities often appear to be unlimited.

Measured service

Resource use is automatically controlled and optimized through metering capabilities, appropriate to type of service (e.g., storage, processing, bandwidth, and active user accounts).

Note: A customer may itself be a cloud and clouds may offer services to one another.

Table 2. Cloud Service Models

Service Model

Provided Capability

No Control On

Control On

Software as a Service

Usage of applications that run on the cloud infrastructure.

Underlying cloud infrastructure – network, servers, operating systems, storage, or individual application capabilities.

Limited application configuration settings.

Platform as a Service

Deployment of applications on the cloud infrastructure; may use supported programming languages, libraries, services, and tools.

Underlying cloud infrastructure – network, servers, operating systems, or storage.

Deployed applications and their environment settings.

Infrastructure as a Service

Provisioning of processing, storage, networks, etc.; may deploy and run operating systems, applications, etc.

Underlying cloud infrastructure.

Operating systems, storage, and deployed applications.

Table 3. Cloud Deployment Models

Deployment Model

Cloud Infrastructure Is For Use By

Owned, Managed, Operated By

Exists on/off premises of cloud provider

Private cloud
(on-site or outsourced)

One organization with multiple consumers (business units).

The organization, a third party, or a combination of them.

On or off premises.

Community cloud
(on-site or outsourced)

Community of consumers from organizations with shared concerns (mission, security, policy, compliance, etc.).

Some of community organizations, a third party, or some combination of them.

On or off premises.

Public cloud

General public.

A business, academic, or government organization, or some combination of them.

On premises.

Hybrid cloud

Consumers from a composition of private/community/public clouds, bounded by technology that enables data and application portability (e.g. cloud bursting).

One of the authors of the NIST definition of CC, Peter Mell, advises the definition to be used as a tool for determining to what extent considered information technology (IT) implementations meet the cloud characteristics and models, as adopting an authentic cloud is a key to reaping cloud benefits such as cost savings, energy savings, rapid deployment, and customer empowerment. Also matching the implementation to the cloud definition can assist in evaluating the security properties of the cloud.

Anyone have ideas or sources on how Cloud Computing is being or should be defined? Please share here!

In next posts, the different cloud computing technologies and configurations will be further explained, and methods and approaches for organizations to consider when making decisions about implementing CC will be recommended.



Irena Bojanova, Ph.D., is the Founding Chair of IEEE CS Cloud Computing STC, an Associate Editor of IEEE Transactions on Cloud Computing, and an Editorial Board member of IEEE CS IT Professional. She is a Professor and Program Director, Information and Technology Systems, at University of Maryland University College, managed academic programs at Johns Hopkins University and PIsoft Ltd., and co-started OBS Ltd., (now CSC Bulgaria). Her current research interests include cloud computing, web-based systems, and educational innovations. She is a member of the IEEE and can be reached at


Cloud Computing Special Technical Community

The Cloud Computing Special Technical Community (CC STC) focuses on Cloud activities across Computer Society (CS).  Its work is complementary to the IEEE Cloud Computing Initiative (IEEE CCI), a 3-year project to promote Cloud efforts across IEEE.

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Open for CS members and non-members.

If you are involved in cloud computing, joining the CC STC will give you chance to contribute your expertise as well as to expand your knowledge by working with others in this field. We have working groups on Conferences, Publications, Cloud Guide, Cloud Testbed, Education, Standards, Newsletter, and Online Presence.

  • To become a member, visit our website and click on the JOIN button.
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Irena Bojanova, Chair CS CC STC 

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