Three-tier
<architecture> A
client-server architecture in which the
user interface, functional process logic ("business rules") and data storage and access are developed and maintained as independent modules, most often on separate platforms.
Apart from the usual advantages of modular software with well defined interfaces, the three-tier architecture is intended to allow any of the three tiers to be upgraded or replaced independently as requirements or technology change.
For example, an upgrade of desktop
operating system from
Microsoft Windows to
Unix would only affect the
user interface code.
Typically, the user interface runs on a desktop
PC or
workstation and uses a standard
graphical user interface, functional process logic may consist of one or more separate modules running on a
workstation or application
server, and an
RDBMS on a database server or
mainframe contains the data storage logic.
The middle tier may be multi-tiered itself (in which case the overall architecture is called an "n-tier architecture").
