The much-hyped but poorly defined terms Web 2.0, Rich Internet Application (RIA) and Ajax are best understood when they are defined together.

Buzzwords represent job security for entrepreneurs like me who would be practically unemployable were it not for our secret knowledge of the true meaning of words like Web 2.0. However, even I must admit that these Buzzwords 2.0 get in the way of clear communication.

In addition, while there are many standalone definitions of terms like Web 2.0, it is much easier to understand these buzzwords mean by considering them together. With that in mind, here are my definitions of Web 2.0, Rich Internet Application and Ajax, complete with helpful graphics:

• Web 2.0 represents a market shift in consumer attention from expert-generated content (Yahoo) to user-generated content (Google)
• Rich Internet Applications represents a requirements shift for more interactive, PC-like web sites to simplify consumer creation of content (Blogger, MySpace)
• Ajax is an architectural shift to support RIA requirements

Definition of Web 2.0 - Shift In Consumer Attention

Consumer eyeballs still rule the web. The huge power shift over the last 5 years has been from expert-driven content (which could be created using expert tools like Adobe Dreamweaver) to user-driven content (which requires web based tools that are easy to use). The shift in consumer attention is also driving a shift in business focus as corporations look at ways to engage more effectively with their customers and employees.

Definition of Rich Internet Application - Shift in Web Requirements

In order for more people to participate in creating content for the Internet, the content creation tools have to be both simpler and more interactive. Rich Internet Applications seek to erase the difference in user experience between browser-based applications (Gmail) and traditional client/server applications (Outlook). A quick comparison of Gmail versus Outlook shows that RIAs have a big usability gap, but the Internet brings the offsetting benefit of dramatically simpler application distribution.

Definition of Ajax - Shift in Web Architecture

Ajax is an architecture which makes the browser smarter and more interactive by running Javascript programs on the client. Don't tell anyone, but the old name for putting logic on the client was fat client programming. Everything old is new again and it turns out the only way to make an interactive client is to do more processing in the browser.

The following diagram shows the fundamental changes between the Web 1.0 architecture (circa 2000) and the Ajax architecture.

Where is all of this leading?

Web 2.0 is driving new application requirements and in turn creating a demand for new development tools that can meet those application requirements. Building increasingly visual and interactive web applications requires a WYSIWYG Ajax tool - something like a Microsoft Access for the Web. Flex and Silverlight, Adobe and Microsoft are providing proprietary tools for building RIA applications.

For an example of an open-source tool for building RIA applications based on Spring, Hibernate and Dojo, check out WaveMaker . Download Wavemaker to see what a visual Ajax tool looks like! Wikipedia also lists a number of other Ajax frameworks for building RIA applications.

References
A number of others have gone before me in defining these terms individually. Jonathan Schwartz recently pointed out that Java has always had RIA capabilities (but he also admits they didn't work very well until recently). Here are my personal favorites definitions:

• Web 2.0. Tim O'Reilly at O'Reilly Media has a good definition of what is web 2.0
• Rich Internet Application. Adobe initially defined the term rich internet application. The Burton Group also has a good white paper on Ajax and RIA (registration required).
  
• Ajax. Jesse James Garrett of Adaptive Path originally defined Ajax.