A multi-tiered client/server application is partitioned into logical units, called tiers, which run in conjunction on separate machines. Multi-tiered applications share data and communicate with one another over a local-area network or even over the Internet. They provide many benefits, such as centralized business logic and thin client applications. 

In its simplest form, sometimes called the "three-tiered model," a multi-tiered application is partitioned into thirds:

• Client application: provides a user interface on the user's machine.
• Application server: resides in a central networking location accessible to all clients and provides common data services.
• Remote database server: provides the relational database management system (RDBMS).

In this three-tiered model, the application server manages the flow of data between clients and the remote database server, so it is sometimes called a "data broker." You usually only create the application server and its clients, although, if you are really ambitious, you could create your own database back end as well. 

In more complex multi-tiered applications, additional services reside between a client and a remote database server. For example, there might be a security services broker to handle secure Internet transactions, or bridge services to handle sharing of data with databases on other platforms. 

Support for developing multi-tiered applications is an extension of the way client datasets communicate with a provider component using transportable data packets. See Understanding multi-tiered database applications for an overview of this technology and the architecture of a typical three-tiered application. Once you understand how to create and manage a three-tiered application, you can create and add additional service layers based on your needs. 

Building a multi-tiered application provides details on how to apply this architecture to build a three-tiered application. Writing Web-based client applications describes how to combine this architecture with other technologies to create a Web-based multi-tiered application.