A new breed of I.T. professionals are brewing nowadays.  They are called “devigners”…These individuals have learned to fuse both design and development to create Rich Internet Applications.  With the market headed towards RIA’s wouldn’t you want to create a stateful client where significant changes to the view would not require to reload another page?

Web Applications present data within web pages that appear within a browser.  These web pages provide an easy way for users to interact with data.

Web Apps typically consist of a number of different layers

• The user interface layer:  Provides the means for a user to interact with the data in the web application.  It usually consists of web pages that include standard elements such as buttons, text inputs, drop-down lists, images, and hyperlinks.
• The data used to populate the user interface
• A third layer that allows the user interface to interact with the data layer.

These layers are often called n-tier or multi-tier architecture.  In n-tier architecture, the user interface is referred to as the presentation tier or layr.  In web applications, the presentation layer occurs withing hte web browser using XHTML or SWF objexts, and client - side scripting such as JavaScript or Actionscript.

The user interface displays data from databases, XML, and text documents, the file system, and data streams from web services and RSS feeds.  Increasingly, web applications rely on XML structures to provide content.  The XML content might just result from a request to a database or by receiving a response from a web service.

This layer is called the data tier in n-tier architecture.  The layer is abstracted from the presentation tier and is located separately.  A database  server provides a good example of the data tier.  It exists separately from the web browser and server.

To include data from the data tier within the presentation tier, there is a need for a middle layer between the two.  In n-tier architecture, this layer is called the business logic, or application tier.  This tier exist as an itermediary between the data source and the application interface.  It also enforces business rules and other logic required within the web application.

The business logic tier exist within an application server and relies on server side languages, such as ColdFusion, ASP.NET, and PHP.  This layer is responsible for requesting data from the data tier and providing it to the presentation tier in an appropriate format, often using an XML structure.

One implication of using n-tier architecture is that this approach separates the presentation layer form the data source.  It’s not possible for the client software to communicate directly with a database.  Instead, the communication between the two is handled with a server side language and an application or web server withing the business logic tier.

PART II (Coming) - How flex fits into an n-tier architectural style….