Where Are Business Objects In An N-Tier Application?
First, it is easier to say where the business object is not. • It is not the user interface (UI) that is the top layer in the application. • It is not the database services or the bottom layer of an application. Business objects reside “in the middle” below the UI that creates the visual presentation and responds to the user’s actions and above the database services layer (i.e., DBMS) that manages the physical data structures. Sounds simple enough, but the definition does beg an answer to the question “What is a layer?” In a layered application design, as shown in Figure 1, communication only occurs between adjacent layers and never skips a layer. For example, the UI communicates directly with the business object and never interacts with the database service layer while the business object, being in the middle, communicates with both the UI and the database services layer. Figure 1. Application Design Layers Layers within an application design are distinct from the layers or tiers pres
