Explain three tier system of salesforce?

MVC

M- model, V-View, C-Controller

Two-tier describes salesforce.com when using an API. The server provides the model and business logic services, while the client provides the client business logic and/or a view. This includes Visualforce that is AJAX-only, where the page is rendered by JavaScript or HTML, and all database calls are handled through JavaScript only. Mobile applications may also be considered in this category when using a native app.

Three-tier can describe salesforce.com when using the GUI. The model provides database and business logic services, the controller can provide business and view logic services, and the view provides the graphical interface. The controller may be a standard controller, a hybrid of standard and custom controllers, or a pure custom controller.

Four-tier describes the model salesforce.com uses most accurately; each tier can be individually tweaked or even replaced without necessarily needing to alter the other tiers, which is a requirement to be classified as a four-tier system. The model can have fields added, for example, without altering the other three layers. Similarly, a new database trigger can be added to the business logic layer without necessarily having to change the model, page controllers, or pages.

The four-tier model is important to note because it is possible to interact with just certain layers. For example, you can truncate the model's data, or mass update a picklist value, without interacting directly with the business logic layer. By using the API, you can bypass the controller logic and view without bypassing the business logic or model. And, of course, you can build an application that treats salesforce.com as one layer of its own two or three-layer architecture.

So, when you're asked if salesforce.com is a two-tier or three-tier application, you can say, "Well, actually, it uses four tiers." ... Or just stick with three-tier, since more people understand that than a four-tier system; just remember that MVC doesn't exactly describe the system 100%. It's more complex than that.

• This reply was modified 6 years, 11 months ago by  Achintya.