three-tier

three-tier

(architecture)A client-server architecture in which theuser interface, functional process logic ("business rules")and data storage and access are developed and maintained asindependent modules, most often on separate platforms.

Apart from the usual advantages of modular software with welldefined interfaces, the three-tier architecture is intended toallow any of the three tiers to be upgraded or replacedindependently as requirements or technology change. Forexample, an upgrade of desktop operating system fromMicrosoft Windows to Unix would only affect the user interface code.

Typically, the user interface runs on a desktop PC orworkstation and uses a standard graphical user interface,functional process logic may consist of one or more separatemodules running on a workstation or application server,and an RDBMS on a database server or mainframe containsthe data storage logic. The middle tier may be multi-tiereditself (in which case the overall architecture is called an"n-tier architecture").