什么是SaaS （Software as a service ）
把软件作为一个服务。SaaS是一种cloud-based 和通过Internet提供软件的模式，用户不用再购买软件，而改用向提供商租用基于Web的软件，且无需对软件进行维护，服务提供商承担软件的全权管理和维护，包括软件的安全和性能，对于一个购买这个软件的企业来说，这个企业可以用这个软件的API，把它Integrated 到本公司的产品中。它消除了企业重新开发、构建和维护部分应用程序的需要。
The Software as a Service (SaaS) model continues to gain traction across all corners of the business world, and for good reason. Also known as on-demand software, hosted software or web-based software, SaaS eschews traditional software installation, maintenance and management approaches in favor of delivering cloud-based applications via the internet. With SaaS, service provider partners shoulder the burdens of security, availability and performance.
Distribution approach. The most important business model characteristic is the distribution approach that a company uses to provide services or create products for customers. We distinguish three main distribution approaches that can be used: on-premise, cloud, and hybrid.
On-premises software distribution approach
The on-premises distribution approach entails a software product being installed and running within a client’s in-house infrastructure, be that a single computer or a local server. The traditional distribution approach has been used for many years by such companies as SAP, Oracle, and Microsoft.
Cloud-based software distribution approach
The main characteristic of the cloud-based distribution approach is that the software runs at a hosting provider or in the cloud service.
For instance, software as a service (SaaS) is a cloud-based distribution approach in which a provider hosts its applications and makes them available to customers via the Internet. According to the SaaS method, businesses and individuals don’t need to install applications on their own computers or own data centers. They can access the software using a Web browser or a mobile device. SaaS is typically delivered via a term-based subscription.
SaaS removes the need for organizations to install and run applications on their own computers or in their own data centers. This eliminates the expense of hardware acquisition, provisioning and maintenance, as well as software licensing, installation and support.
Hybrid software distribution approach
Some software companies have a hybrid distribution approach. Hybrid in this case is the approach that combines a SaaS solution with an on-premise software application. So, a cloud-driven technology complements an on-premise one. For instance, Adobe Creative Cloud combines on-premise products like Photoshop with additional cloud services like libraries, presets, etc. Besides, on-premise software gets updated as if deployed on the cloud, regularly and without asking the client to purchase a separate license for each new version of a product. As high-speed Internet connection has become a new standard, hybrids will become increasingly more common.
Another way to realize the hybrid deployment is to let customers choose between a SaaS service or an on-premises solution and provide the opportunity to switch from one to the other if needed. For example, Microsoft Outlook can be deployed on-premises but can also be accessed online.