Software-as-a-Service #

The traditional model of software distribution, in which software is purchased for and installed on personal computers, is sometimes referred to as Software-as-a- Product. Software-as-a-Service is a software distribution model in which applications are hosted by a vendor or service provider and made available to customers over a network, typically the Internet. SaaS is becoming an increasingly prevalent delivery model as underlying technologies that support web services and service-oriented architecture (SOA) mature and new developmental approaches become popular. SaaS is also often associated with a pay-as-you-go subscription licensing model. Meanwhile, broadband service has become increasingly available to support user access from more areas around the world.

International Data Corportation identifies two slightly different delivery models for SaaS.

The  hosted  application  management  model  is  similar  to  an   Application  Service Provider (ASP) model. Here, an ASP hosts commercially available software for customers and delivers it over the Internet. The other model is a software on demand model where the provider gives customers network-based access to a single copy of an application created specifically for SaaS distribution.

SaaS is most often implemented to provide business software functionality to enterprise customers at a low cost while allowing those customers to obtain the same benefits of commercially licensed, internally operated software without the associated complexity of installation, management, support, licensing, and high initial cost. Most customers have little interest in the how or why of software implementation, deployment, etc., but all have a need to use software in their work. Many types of software are well suited to the SaaS model (e.g., accounting, customer relationship management, email software, human resources, IT security, IT service management, video conferencing, web analytics, web content management). The distinction between SaaS and earlier applications delivered over the Internet is that SaaS solutions were developed specifically to work within a web browser. The architecture of SaaS-based applications is specifically designed to support many concurrent users (multitenancy) at once. This is a big difference from the traditional client/server or application service provider (ASP)- based solutions that cater to a contained audience. SaaS providers, on the other hand, leverage enormous economies of scale in the deployment, management, support, and maintenance of their offerings.

Key Characteristics of PaaS
SaaS Implementation Issues