Presentation tier

The presentation tier provides functionality for the application's UI. It should provide an appealing visual design as it is the part of the application that users interact with and see. Data is presented to the user and input is received from users in this tier. Aspects of the usability quality attribute, which were discussed in Chapter 4, Software Quality Attributes, should be the concern of the presentation tier.

This tier should contain logic to render the user interface, including the placement of data in the appropriate UI components, formatting the data that is presented appropriately, and hiding/showing UI components as required.

It should also provide some basic validation to help users avoid or minimize mistakes, such as ensuring the correct type of data is being entered for a given control and that the data is in the correct format. Developers should be careful not to introduce business logic into the validation, which should be handled by the business tier.

The presentation tier should provide users with useful feedback, such as friendly and informative messages, tooltips, visual feedback, such as a progress bar for long-running processes, and notifications to inform users about the completion or failure of asynchronous operations.

Software architects should strive to design thin clients that minimize the amount of logic that exists in the presentation tier. The logic in the presentation tier should focus on user interface concerns. A presentation tier devoid of business logic will be easier to test.