XML by Example

In most cases, but not in this example, the rightmost server is a database

server and is therefore often called the data tier.

N-Tiers

It’s possible to add more parties to the application by chaining together

more client/server applications. For example, some email servers depend on

a database. The Webmail application would look like Figure 11.3 where

there are four parties or tiers.

348

Chapter 11: N-Tiered Architecture and XML

EXAMPLE

Figure 11.3: Adding one more tier

As you add more tiers, you can build 5-tiered or 6-tiered applications, or

even more (although having more than four tiers is uncommon). The term

n-tiers is a generic term for client/servers ...