A multi-tier application is used to divide an enterprise application into two or more components that may be separately developed and executed. In general, the tiers in a multi-tier application include the following:

Presentation tier: Provides basic user interface and application access services

Application processing tier: Possesses the core business or applicationlogic

Data access tier: Provides the mechanism used to access and process data

Data tier: Holds and manages data that is at rest This division allows each

component/tier to be separately developed, tested, executed and reused.