Software as a Service (SaaS)

NIST (2011) defines SaaS as:

With SaaS, a service provider licenses an application to customers either as a service on demand, through a subscription, as a ‘pay-as-you-go’ model, or (increasingly) at no charge when there is opportunity to generate revenue from streams other than from the user, such as from advertisements. SaaS is a rapidly growing market and it is expected that SaaS will soon become commonplace within most organisations.

Advantages of SaaS include:

• the provision of software that would be normally installed on users’ computers (e.g. Microsoft Office) as web applications
• users are not required to implement software upgrades and patches
• the provider can provide scalable web applications using a multi-tiered architecture, implemented on a high-performance infrastructure
• the entire application and hosting infrastructure is the responsibility of the service provider (Figure 4).

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Figure 4 Cloud computing service models depicted as a stack of component layers

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A diagram of four vertical columns of rounded boxes stacked on top of one another. From the left, the first column has 9 boxes, with the following text inside: traditional software, application, runtime environment, middleware, operating system, virtual machines, servers, storage, networking. There is an arrow running vertically along all of these, labelled client manages. The second column has another 9 boxes, with the following text: infrastructure as a service (IaaS), application, runtime environment, middleware, operating system. These boxes have an arrow running vertically alongside them, with the label: client manages. The remaining four boxes in this column have the following text: virtual machines, servers, storage, networking, and these have an arrow running alongside them with the label vendor manages. The third column from the left has 9 boxes, with the following: Platform as a service (PaaS), application, runtime environment, middleware, operating system, virtual machines, servers, storage, networking. There is an arrow running from the application box to the last box, with the label vendor manages. The final column on the right has 9 boxes. There is an arrow running along all of them, with the label vendor manages. The boxes have the following text: Software as a service (SaaS), application, runtime environment, midleware, operating system, virtual machines, servers, storage, networking.

Figure 4 Cloud computing service models depicted as a stack of component layers

With SaaS a significant amount of the processing occurs on service providers’ computers and not on the service consumers’ computers.

There are numerous examples of SaaS available, many based on subscription fees like Netflix and DropBox. Organisations can also use the SaaS model to provide email, word processing and other ‘office’ tools for their employees. A recent trend is for application developers to convert from stand-alone applications to a web-based SaaS delivery model. For example, Microsoft Office 365 is a group of software and service subscriptions which together provide access to Microsoft Office applications and cloud storage services to subscribers. The SaaS model gives the developer greater control since they deploy to a known environment in the cloud rather than distributing thousands of copies to individual users.