three-tier

A three-tier model still involves a client and server, but there is another tier where the data repository usually resides. This third tier may be on the server, a second server, or maybe even a cluster of other servers. The general idea is that the client will request data from the server, the server will get the data from the data tier, package it up and send it to the client. Again, a web page example works well for this model, especially when considering server-side scripting and a database back-end. The web browser requests a web page, the web server accepts the requests, and the server-side script on the web server communicates with the database server to retrieve the data. The server-side script then packages up the data into HTML which is sent back to the client.