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 userinterface 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").

(1998-05-13)