MACROMEDIA FLEX-GETTING STARTED WITH FLEX Getting Started page 8

Using Flex in an n-tier application model
By definition, enterprise applications are multitiered, where each tier brings specific benefits to
the application design. A tiered architecture provides natural access points for integration with
existing and future systems.
Each tier serves a specific purpose, and lets you divide the functionality of a business application
into discrete components that you can implement independently from each other. For example,
the following figure shows the tiers of a five-tier application model:
Application clients, Flash, applets, and other GUIs
ASP, JSP, Servlets, and other UI elements
Connects to business objects
Connects to data and legacy systems
Databases, external systems, and legacy resources
An n-tier architecture offers the following advantages:
•
The tiers, or even components of the tiers, can be distributed across multiple hardware systems
to improve system scalability and performance.
•
The client and presentation tiers shield clients from the complexities of accessing the enterprise
data store.
•
You can distribute application development across your development group. For example, JSP
developers are typically concerned with information presentation rather than with
implementing business rules. Conversely, EJB developers are concerned with data access and
manipulation, but not with presentation.
In traditional n-tier applications, the presentation tier logic executes on the server, so every client
interaction requires a data transfer between the client and server.
8 Chapter 1: Introducing Flex
Client Tier
Presentation Tier
Business Tier
Integration Tier
Resource Tier
Running on client
Running on server