Three-Tiered Application Model
- Presentation - The client consists mostly of a graphical user interface (GUI) such as a browser used to display Web pages. Services such as database connection and business services obtained from middle-tier servers. It results in less overhead for the user, but more network traffic for the system as components distributed among different machines.
- Business /Data Components - Middle tier components can implement data rules or business rules. These components provide the logic between the client computer and the data source. It is the layer where necessary line-of-business standards and logic exist. Business rules can consist of business algorithms or legal or government regulations. Data rules consist of rules to keep the data structures consistent, within a particular database as well as among multiple databases. These components can exist on a server computer to assist in resource sharing. They can be used to enforce business and data rules. Since they are not tied to a particular client, they can be employed by all applications.
- Data Source - The data source tier represents a computer running a database where information stored. It is the actual database management system (DBMS) access layer. You can access the data source tier though the data/business rules layer, and on occasion directly through the presentation layer itself. The data source tier consists of data access components (rather than raw DBMS connections)*to aid in resource sharing and to allow clients configured without installing an application comprised of libraries or drivers on each client.
ActiveX Language Support
If a client encountered a component with enhanced functionality when it was expecting a component with only a base level of functionality, such as an older version of the component, it would not fail. It is because it has no dependency on the newer features.