Access to Legacy Applications and Data

Three-Tier Applications and Middleware

A three-tier application divides a networked application into three logical areas. Middleware, such as Component Services, connects the three tiers: presentation, business logic, and data processing.

Tier 1 handles presentation. In a Web application, data is requested by the browser and is sent there from the Web server for display.

Tier 2 processes business logic (the set of rules for processing business information). In an IIS 5.0–based Web application, Tier 2 processing is carried out using components of IIS 5.0.

Tier 3 processes the data (the associated databases and files where the data is stored). In a Web application, Tier 3 consists of a back-end database management system (DBMS) or a file access system with its associated data.

Three-tier systems are easier to modify and maintain than two-tier systems because the programming of presentation, business logic, and data processing are separated by design. This architecture permits redevelopment to proceed in one tier, without affecting the others.

Middleware, such as Component Services, makes efficient use of resources so that Web application programmers can concentrate on business logic. Component Services can connect the browser request (Tier 1) to the business logic (Tier 2). In Tier 3, it can connect business logic to the databases and manage all activities of the transaction.