Software Architect's Handbook

Business tier

The business tier, which is sometimes referred to as the application tier, provides the implementation for the business logic of the application, including such things as business rules, validations, and calculation logic. Business entities for the application's domain are placed in this tier.

The business tier coordinates the application and executes logic. It can perform detailed processes and makes logical decisions. The business tier is the center of the application and serves as an intermediary between the presentation and data tiers. It provides the presentation tier with services, commands, and data that it can use, and it interacts with the data tier to retrieve and manipulate data.