1.2.1 Design Philosophy in Application Development

Interstage Studio adopts the three-tier model as the design philosophy for system development of Web applications and Web services.

Three-tier model

The design philosophy realized by the three-tier model has processing in a system logically divided into three processing logic layers, as listed below, for development and operation. These processing logic layers are flexibly distributed and linked together using open technologies.

Table 1.2 Classification of logic layers in the three-tier model
Processing logic layer	Description
Presentation logic	Controls all user interfaces. For example, its processing includes: Displaying an initial screen to a user Receiving information entered by a user and checking the information at the syntax level Displaying processing results and other information
Business logic	Executes processing of the application itself according to user's instructions received from screen display control. For example, its processing includes: Financial accounting Inventory control and related tasks If necessary, this layer is linked with the database logic layer to perform database operations.
Database logic	Performs database operations according to instructions from the business logic layer. This layer guarantees database consistency and executes reference, update, and other database processing tasks. Normally, the database management system (DBMS), such as Symfoware or Oracle, processes the tasks.

The figure below outlines the three-tier model.

Figure 1.3 Outline of application development using the three-tier model

By distributing the process logic layers as follows, the three-tier model enables development of an efficient system that has high scalability and maintainability:

Presentation logic (screen display control, etc.)
Clients
Business logic
Application server
Database logic
Database server

The application server provides an execution environment for business logic and linkage between applications.