Three-Tiered Applications

To use Remote Data Service technology, you must understand the three-tiered client/server model. This model separates the various components of a client/server system into three "tiers":

• Client tier—a local computer on which either a Web browser displays a Web page that can display and manipulate data from a remote data source, or (in non–Web-based applications) a stand-alone compiled front-end application.
  
  
• Middle tier—a Microsoft^® Windows NT^® Server computer that hosts components that encapsulate an organization's business rules. Middle-tier components can be either Active Server Page scripts executed on Internet Information Server, or (in non–Web-based applications) compiled executables.
  
  
• Data source tier—a computer hosting a database management system (DBMS), such as a Microsoft^® SQL Server™ database. (In a two-tier application, the middle tier and data source tier are combined.)

These tiers don't necessarily correspond to physical locations on the network. For example, all three tiers may exist on only two computers. One computer could be a Microsoft^® Windows^® 95 computer running Microsoft^® Internet Explorer 4.0 as its browser. The second computer could be a Windows NT Server computer running both Internet Information Server and Microsoft SQL Server. Designing applications this way gives you greater flexibility when deploying processes and data on the network for maximum performance and ease of maintenance.