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.