the user interface, functional process logic ("business rules"),
computer data storage and data access
are developed and maintained as independent modules,
most often on separate platforms.
Three-tier architecture has the following three tiers:
1. Presentation tier
This is the topmost level of the application.
The presentation tier displays information related to
such services as browsing merchandise, purchasing,
and shopping cart contents.
It communicates with other tiers by outputting results to
the browser/client tier and all other tiers in the network.
2. Application tier
(business logic, logic tier, data access tier, or middle tier)
The logic tier is pulled out from the presentation tier and,
as its own layer,
it controls an application's functionality by performing detailed processing.
3. Data tier
This tier consists of database servers.
Here information is stored and retrieved.
This tier keeps data neutral and independent
from application servers or business logic.
Giving data its own tier also improves scalability and performance.
Sumber:
* http://en.wikipedia.org/wiki/N_tier
* http://en.wikipedia.org/wiki/File:Overview_of_a_three-tier_application_vectorVersion.svg
